gh-15154: Fixed stale containers trying to sync across devices (gh-15166)

gh-15163: Sync upstream Firefox to version 155.0 RC (gh-15164)
gh-14380: Fix sidebar width getting stuck when toggling layout on the right side (gh-15092)
2026-08-30 18:31:30 +00:00 · 2026-08-30 00:42:45 +02:00 · 2026-08-30 00:26:45 +02:00 · 2026-08-29 12:35:31 +02:00 · 2026-08-29 12:35:17 +02:00 · 2026-08-29 01:34:29 +02:00
621 changed files with 87080 additions and 1414 deletions
--- a/.gitattributes
+++ b/.gitattributes
@@ -5,4 +5,4 @@
 *.patch linguist-language=C++
 *.d.ts linguist-language=TypeScript

-src/zen/tests/*.js linguist-language=Test
+src/zen/tests/** linguist-language=C++
--- a/.github/workflows/linux-release-build.yml
+++ b/.github/workflows/linux-release-build.yml
@@ -105,6 +105,8 @@ jobs:
          SURFER_COMPAT: ${{ matrix.arch }}
          SURFER_CERT_PATCH_ISSUER: ${{ secrets.SURFER_CERT_PATCH_ISSUER }}
          SURFER_CERT_PATCH_NAME: ${{ secrets.SURFER_CERT_PATCH_NAME }}
+          SURFER_CERT_PATCH_NAME_PREV: ${{ secrets.SURFER_CERT_PATCH_NAME_PREV }}
+          SURFER_CERT_PATCH_ISSUER_PREV: ${{ secrets.SURFER_CERT_PATCH_ISSUER_PREV }}
        run: |
          . "$HOME/.cargo/env"
          npm run import
--- a/.github/workflows/macos-release-build.yml
+++ b/.github/workflows/macos-release-build.yml
@@ -122,6 +122,8 @@ jobs:
          SURFER_COMPAT: ${{ matrix.arch }}
          SURFER_CERT_PATCH_ISSUER: ${{ secrets.SURFER_CERT_PATCH_ISSUER }}
          SURFER_CERT_PATCH_NAME: ${{ secrets.SURFER_CERT_PATCH_NAME }}
+          SURFER_CERT_PATCH_NAME_PREV: ${{ secrets.SURFER_CERT_PATCH_NAME_PREV }}
+          SURFER_CERT_PATCH_ISSUER_PREV: ${{ secrets.SURFER_CERT_PATCH_ISSUER_PREV }}
          SURFER_PLATFORM: darwin
        run: |
          . "$HOME/.cargo/env"
--- a/.github/workflows/windows-release-build.yml
+++ b/.github/workflows/windows-release-build.yml
@@ -166,6 +166,8 @@ jobs:
          SURFER_COMPAT: ${{ matrix.arch }}
          SURFER_CERT_PATCH_ISSUER: ${{ secrets.SURFER_CERT_PATCH_ISSUER }}
          SURFER_CERT_PATCH_NAME: ${{ secrets.SURFER_CERT_PATCH_NAME }}
+          SURFER_CERT_PATCH_NAME_PREV: ${{ secrets.SURFER_CERT_PATCH_NAME_PREV }}
+          SURFER_CERT_PATCH_ISSUER_PREV: ${{ secrets.SURFER_CERT_PATCH_ISSUER_PREV }}
        run: |
          . "$HOME/.cargo/env"
          npm run import -- --verbose
--- a/README.md
+++ b/README.md
@@ -34,8 +34,8 @@ Zen is a firefox-based browser with the aim of pushing your productivity to a ne

 ### Firefox Versions

- [`Release`](https://zen-browser.app/download) - Is currently built using Firefox version `154.0`! 🚀
- [`Twilight`](https://zen-browser.app/download?twilight) - Is currently built using Firefox version `RC 154.0`!
+- [`Release`](https://zen-browser.app/download) - Is currently built using Firefox version `154.0.1`!
+- [`Twilight`](https://zen-browser.app/download?twilight) - Is currently built using Firefox version `RC 155.0`!

 ### Contributing

--- a/build/firefox-cache/l10n-last-commit-hash
+++ b/build/firefox-cache/l10n-last-commit-hash
@@ -1 +1 @@
-1fb0703fa9723fd9c400ad60d18e64ee4f9bf125
+6b4abe0093721c1be89eb41b3fb060dd6336923d
--- a/build/windows/sign.ps1
+++ b/build/windows/sign.ps1
@@ -3,8 +3,6 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.

 param(
-    [string][Parameter(Mandatory=$true)]$SignIdentity,
-    [string][Parameter(Mandatory=$true)]$SignIdentityIssuer,
    [string][Parameter(Mandatory=$true)]$GithubRunId
 )

@@ -24,11 +22,15 @@ mkdir windsign-temp -ErrorAction SilentlyContinue
 #    echo "Downloaded git objects repo to"
 #} -Verbose -ArgumentList $PWD -Debug

+$token = gh auth token
+
 $env:SURFER_MOZCONFIG_ONLY="1"
 $env:SURFER_SIGNING_MODE=""

-$env:SURFER_CERT_PATCH_ISSUER=$SignIdentityIssuer
-$env:SURFER_CERT_PATCH_NAME=$SignIdentity
+get-content "$PSScriptRoot/../.env" | foreach {
+    $name, $value = $_.split('=')
+    set-content env:\$name $value
+}

 Start-Job -Name "DownloadGitl10n" -ScriptBlock {
    param($PWD)
@@ -46,7 +48,6 @@ npm run build

 echo "Downloading artifacts info"
 $artifactsInfo=gh api repos/zen-browser/desktop/actions/runs/$GithubRunId/artifacts
-$token = gh auth token

 function New-TemporaryDirectory {
    $tmp = [System.IO.Path]::GetTempPath() # Not $env:TEMP, see https://stackoverflow.com/a/946017
--- a/locales/en-US/browser/browser/zen-general.ftl
+++ b/locales/en-US/browser/browser/zen-general.ftl
@@ -164,5 +164,5 @@ zen-window-sync-migration-dialog-learn-more = Learn More
 zen-window-sync-migration-dialog-accept = Got It

 zen-appmenu-new-blank-window =
-    .label = New blank window
+    .label = New Blank Window

--- a/locales/en-US/browser/browser/zen-split-view.ftl
+++ b/locales/en-US/browser/browser/zen-split-view.ftl
@@ -5,14 +5,14 @@
 tab-zen-split-tabs =
    .label =
        { $tabCount ->
-            [-1] Split out tab
-            [1] Add split view...
+            [-1] Split Out Tab
+            [1] Add Split View...
           *[other] Join { $tabCount } Tabs
        }
    .accesskey = S

 zen-split-link =
-    .label = Split link to new tab
+    .label = Split Link to New Tab
    .accesskey = S

 zen-split-view-modifier-header = Split View
--- a/locales/en-US/browser/browser/zen-workspaces.ftl
+++ b/locales/en-US/browser/browser/zen-workspaces.ftl
@@ -86,6 +86,8 @@ zen-workspace-default-profile = Default

 zen-workspaces-delete-workspace-title = Delete Space?
 zen-workspaces-delete-workspace-body = Are you sure you want to delete { $name }? This action cannot be undone.
+zen-workspaces-remote-delete-title = Delete Synced Space?
+zen-workspaces-remote-delete-body = { $name } was deleted on another device. Delete it here too? Keeping it will restore it on your other devices.

 # Note that the html tag MUST not be changed or removed, as it is used to better
 # display the shortcut in the toast notification.
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,7 +11,7 @@
      "devDependencies": {
        "@babel/preset-typescript": "^7.27.0",
        "@zen-browser/prettier": "^3.9.3",
-        "@zen-browser/surfer": "^1.14.7",
+        "@zen-browser/surfer": "^1.14.8",
        "formal-git": "^1.2.9",
        "globals": "^16.3.0",
        "husky": "^9.1.7",
@@ -860,9 +860,9 @@
      }
    },
    "node_modules/@zen-browser/surfer": {
-      "version": "1.14.7",
-      "resolved": "https://registry.npmjs.org/@zen-browser/surfer/-/surfer-1.14.7.tgz",
-      "integrity": "sha512-Ui2Chqvr4/+FmHM54eKOv7cQu8DRAK/uCX9o1GNi81hszxo/RSQwaw71eNW43Qcj7giK4U4x0IdCMht98iQ0rA==",
+      "version": "1.14.8",
+      "resolved": "https://registry.npmjs.org/@zen-browser/surfer/-/surfer-1.14.8.tgz",
+      "integrity": "sha512-5HHcfibwHIK5n3huhJL2TLBX2+8odj6ebCMA6U2EcUj9ROSrcz7/bjY2n5MIa9oIRL9gtV3ott0jwJj6SlapxA==",
      "dev": true,
      "license": "MPL-2.0",
      "dependencies": {
--- a/package.json
+++ b/package.json
@@ -49,7 +49,7 @@
  "devDependencies": {
    "@babel/preset-typescript": "^7.27.0",
    "@zen-browser/prettier": "^3.9.3",
-    "@zen-browser/surfer": "^1.14.7",
+    "@zen-browser/surfer": "^1.14.8",
    "formal-git": "^1.2.9",
    "globals": "^16.3.0",
    "husky": "^9.1.7",
--- a/prefs/firefox/browser.yaml
+++ b/prefs/firefox/browser.yaml
@@ -95,6 +95,9 @@
 - name: browser.search.widget.new
  value: true

+- name: layout.css.corner-shape.enabled
+  value: true
+
 # Disabled from https://searchfox.org/firefox-main/rev/d6bfff43852356ca98af848b4705d37f8d41856f/modules/libpref/init/StaticPrefList.yaml#2008
 # Only enabled for windows, doesn't really fit inside Zen.
 - name: browser.startup.preXulSkeletonUI
--- a/prefs/zen/sync.yaml
+++ b/prefs/zen/sync.yaml
@@ -10,3 +10,6 @@
  value: false
  locked: true
  condition: "!@IS_TWILIGHT@"
+
+- name: zen.spaces-sync.debug
+  value: false
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,4 +8,4 @@ packaging==24.2
 pathspec==0.12.1
 platformdirs==4.3.6
 pycodestyle==2.12.1
-requests==2.33.0
+requests==2.34.2
--- a/src/-prettierignore.patch
+++ b/src/-prettierignore.patch
@@ -1,8 +1,8 @@
 diff --git a/.prettierignore b/.prettierignore
-index 949896ff064ae0b54b6a657ea074bc88e12820f7..5249f420972667bece4d85fe8d35073afaebeb8a 100644
+index bd8ab46ff7175f5039b69b04c1afe53ab8efe746..7ae12a1ff3724e99aeec2e93518640a2fa9611e6 100644
 --- a/.prettierignore
 +++ b/.prettierignore
-@@ -1803,3 +1803,12 @@ tools/ts/test/baselines/
+@@ -1807,3 +1807,12 @@ tools/ts/test/baselines/
 try_task_config.json
 xpcom/idl-parser/xpidl/fixtures/xpctest.d.json
 **/package-lock.json
@@ -12,6 +12,6 @@ index 949896ff064ae0b54b6a657ea074bc88e12820f7..5249f420972667bece4d85fe8d35073a
 +*.min.js
 +*.min.mjs
 +*.inc
-+*/mochitests/*
+**/mochitests/**
 +*.svg
 +
--- a/src/-stylelintrc-js.patch
+++ b/src/-stylelintrc-js.patch
@@ -1,5 +1,5 @@
 diff --git a/.stylelintrc.js b/.stylelintrc.js
-index b484bf6600a7e1b8ad2aed8c8b7fe5e84cc3d023..f89712e2c13dfa0bcb48e55cd3872c67f5c98dad 100644
+index b5f8245fa04ffb8fc82240261d63f893f4629f19..1b6ead24adbe69fcb5aeb95cfd3e7fa9662d89d8 100644
 --- a/.stylelintrc.js
 +++ b/.stylelintrc.js
@@ -67,7 +67,7 @@ module.exports = {
@@ -11,10 +11,10 @@ index b484bf6600a7e1b8ad2aed8c8b7fe5e84cc3d023..f89712e2c13dfa0bcb48e55cd3872c67
       {
         ignore: ["blockless-at-rules"],
       },
-@@ -280,7 +280,7 @@ module.exports = {
-     "media-query-no-invalid": null,
+@@ -281,7 +281,7 @@ module.exports = {
     "stylelint-plugin-mozilla/media-query-no-invalid": true,
     "stylelint-plugin-mozilla/no-base-design-tokens": true,
+     "stylelint-plugin-mozilla/no-has-selector": true,
 -    "stylelint-plugin-mozilla/use-design-tokens": true,
 +    "stylelint-plugin-mozilla/use-design-tokens": false,
   },
--- a/src/browser/base/content/navigator-toolbox-inc-xhtml.patch
+++ b/src/browser/base/content/navigator-toolbox-inc-xhtml.patch
@@ -1,5 +1,5 @@
 diff --git a/browser/base/content/navigator-toolbox.inc.xhtml b/browser/base/content/navigator-toolbox.inc.xhtml
-index dd2f391096968564086911c532f696dc7ffb8ae1..3de617bf4fb7fa35f7d4d7b618e4673b72b953ee 100644
+index dd2f391096968564086911c532f696dc7ffb8ae1..c968e5f0ebb5f0151fb124bafe10d8d5361e060f 100644
 --- a/browser/base/content/navigator-toolbox.inc.xhtml
 +++ b/browser/base/content/navigator-toolbox.inc.xhtml
@@ -2,7 +2,7 @@
@@ -19,7 +19,7 @@ index dd2f391096968564086911c532f696dc7ffb8ae1..3de617bf4fb7fa35f7d4d7b618e4673b
   </toolbar>
 
 +<hbox id="titlebar">
-+  <html:div id="zen-toolbar-background" class="zen-toolbar-background zen-browser-generic-background">
+  <html:div id="zen-toolbar-background" class="zen-toolbar-background zen-squircle-before zen-squircle-after zen-browser-generic-background">
 +    <html:div class="zen-browser-grain" />
 +  </html:div>
 +  <box id="zen-overflow-extensions-list" skipintoolbarset="true" contextmenu="toolbar-context-menu" />
--- a/src/browser/base/content/zen-panels/site-data.inc
+++ b/src/browser/base/content/zen-panels/site-data.inc
@@ -15,19 +15,23 @@
                mainview-with-header="true">
      <hbox id="zen-site-data-header">
        <toolbarbutton id="zen-site-data-header-share"
+                        class="zen-squircle-before"
                        data-l10n-id="zen-site-data-header-share"
                        flex="1"
                        closemenu="none" />
        <toolbarbutton id="zen-site-data-header-reader-mode"
+                        class="zen-squircle-before"
                        data-l10n-id="zen-site-data-header-reader-mode"
                        command="View:ReaderView"
                        tooltip="dynamic-shortcut-tooltip"
                        flex="1" />
        <toolbarbutton id="zen-site-data-header-screenshot"
+                        class="zen-squircle-before"
                        data-l10n-id="zen-site-data-header-screenshot"
                        command="Browser:Screenshot"
                        flex="1" />
        <toolbarbutton id="zen-site-data-header-bookmark"
+                        class="zen-squircle-before"
                        data-l10n-id="zen-site-data-header-bookmark"
                        command="Browser:AddBookmarkAs"
                        flex="1" />
--- a/src/browser/base/content/zen-panels/theme-picker.inc
+++ b/src/browser/base/content/zen-panels/theme-picker.inc
@@ -131,10 +131,10 @@
            </box>
            <html:input type="range" value="0.4" step="0.001" id="PanelUI-zen-gradient-generator-opacity"
 #ifdef XP_MACOSX
-              max="0.9"
+              max="0.8"
              min="0.30"
 #else
-              max="0.9"
+              max="0.8"
              min="0.25"
 #endif
              />
--- a/src/browser/components/customizableui/CustomizableUI-sys-mjs.patch
+++ b/src/browser/components/customizableui/CustomizableUI-sys-mjs.patch
@@ -1,5 +1,5 @@
 diff --git a/browser/components/customizableui/CustomizableUI.sys.mjs b/browser/components/customizableui/CustomizableUI.sys.mjs
-index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2681652e5 100644
+index 6d1885a54815d10b3a4e79f7e5acd61ab3abb159..97e07d85c69ec97baeab05aedd57bd8869254d59 100644
 --- a/browser/components/customizableui/CustomizableUI.sys.mjs
 +++ b/browser/components/customizableui/CustomizableUI.sys.mjs
@@ -13,6 +13,7 @@ ChromeUtils.defineESModuleGetters(lazy, {
@@ -10,7 +10,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
   HomePage: "resource:///modules/HomePage.sys.mjs",
   PanelMultiView:
     "moz-src:///browser/components/customizableui/PanelMultiView.sys.mjs",
-@@ -348,7 +349,7 @@ var CustomizableUIInternal = {
+@@ -352,7 +353,7 @@ var CustomizableUIInternal = {
       {
         type: CustomizableUI.TYPE_PANEL,
         defaultPlacements: [],
@@ -19,7 +19,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
       },
       false
     );
-@@ -358,27 +359,23 @@ var CustomizableUIInternal = {
+@@ -362,27 +363,23 @@ var CustomizableUIInternal = {
       "back-button",
       "forward-button",
       "stop-reload-button",
@@ -50,17 +50,18 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
         defaultCollapsed: false,
       },
       true
-@@ -402,9 +399,6 @@ var CustomizableUIInternal = {
+@@ -406,10 +403,6 @@ var CustomizableUIInternal = {
         type: CustomizableUI.TYPE_TOOLBAR,
         defaultPlacements: [
           "tabbrowser-tabs",
 -          "new-tab-button",
+-          "spring",
 -          "alltabs-button",
 -          "ai-window-toggle",
         ],
         verticalTabsDefaultPlacements: [],
         defaultCollapsed: null,
-@@ -484,6 +478,7 @@ var CustomizableUIInternal = {
+@@ -502,6 +495,7 @@ var CustomizableUIInternal = {
       CustomizableUI.AREA_NAVBAR,
       CustomizableUI.AREA_BOOKMARKS,
       CustomizableUI.AREA_TABSTRIP,
@@ -68,7 +69,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
     ]);
     if (AppConstants.platform != "macosx") {
       toolbars.add(CustomizableUI.AREA_MENUBAR);
-@@ -1285,6 +1280,9 @@ var CustomizableUIInternal = {
+@@ -1334,6 +1328,9 @@ var CustomizableUIInternal = {
         placements = gPlacements.get(area);
       }
 
@@ -78,7 +79,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
       // For toolbars that need it, mark as dirty.
       let defaultPlacements = areaProperties.get("defaultPlacements");
       if (
-@@ -1793,7 +1791,6 @@ var CustomizableUIInternal = {
+@@ -1842,7 +1839,6 @@ var CustomizableUIInternal = {
         lazy.log.info(
           "Widget " + aWidgetId + " not found, unable to remove from " + aArea
         );
@@ -86,7 +87,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
       }
 
       this.notifyDOMChange(widgetNode, null, container, true, () => {
-@@ -1803,7 +1800,7 @@ var CustomizableUIInternal = {
+@@ -1852,7 +1848,7 @@ var CustomizableUIInternal = {
         // We also need to remove the panel context menu if it's there:
         this.ensureButtonContextMenu(widgetNode);
         if (gPalette.has(aWidgetId) || this.isSpecialWidget(aWidgetId)) {
@@ -95,7 +96,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
         } else {
           window.gNavToolbox.palette.appendChild(widgetNode);
         }
-@@ -1971,16 +1968,16 @@ var CustomizableUIInternal = {
+@@ -2020,16 +2016,16 @@ var CustomizableUIInternal = {
         elem.setAttribute("skipintoolbarset", "true");
       }
     }
@@ -115,7 +116,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
     // Handle initial state of vertical tabs.
     if (isVerticalTabs) {
       // Show the vertical tabs toolbar
-@@ -2222,6 +2219,10 @@ var CustomizableUIInternal = {
+@@ -2271,6 +2267,10 @@ var CustomizableUIInternal = {
    *   The identifier string of the area that aNode is being inserted into.
    */
   insertWidgetBefore(aNode, aNextNode, aContainer, aAreaId) {
@@ -126,7 +127,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
     this.notifyDOMChange(aNode, aNextNode, aContainer, false, () => {
       this.setLocationAttributes(aNode, aAreaId);
       aContainer.insertBefore(aNode, aNextNode);
-@@ -4592,7 +4593,7 @@ var CustomizableUIInternal = {
+@@ -4647,7 +4647,7 @@ var CustomizableUIInternal = {
    * For all registered areas, builds those areas to reflect the current
    * placement state of all widgets.
    */
@@ -135,7 +136,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
     for (let [areaId, areaNodes] of gBuildAreas) {
       let placements = gPlacements.get(areaId);
       let isFirstChangedToolbar = true;
-@@ -4603,7 +4604,7 @@ var CustomizableUIInternal = {
+@@ -4658,7 +4658,7 @@ var CustomizableUIInternal = {
         if (area.get("type") == CustomizableUI.TYPE_TOOLBAR) {
           let defaultCollapsed = area.get("defaultCollapsed");
           let win = areaNode.documentGlobal;
@@ -144,7 +145,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
             win.setToolbarVisibility(
               areaNode,
               typeof defaultCollapsed == "string"
-@@ -5899,6 +5900,7 @@ export var CustomizableUI = {
+@@ -5971,6 +5971,7 @@ export var CustomizableUI = {
   unregisterArea(aName, aDestroyPlacements) {
     CustomizableUIInternal.unregisterArea(aName, aDestroyPlacements);
   },
@@ -152,7 +153,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
   /**
    * Add a widget to an area.
    * If the area to which you try to add is not known to CustomizableUI,
-@@ -7869,7 +7871,9 @@ class OverflowableToolbar {
+@@ -7946,7 +7947,9 @@ class OverflowableToolbar {
         );
 
         if (webExtList && CustomizableUI.isWebExtensionWidget(child.id)) {
@@ -162,7 +163,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
           webExtList.insertBefore(child, webExtList.firstElementChild);
         } else {
           child.setAttribute("cui-anchorid", this.#defaultListButton.id);
-@@ -7929,7 +7933,7 @@ class OverflowableToolbar {
+@@ -8006,7 +8009,7 @@ class OverflowableToolbar {
         ) {
           continue;
         }
@@ -171,7 +172,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
         if (child != aExceptChild) {
           sum += getInlineSize(child);
         }
-@@ -7953,11 +7957,11 @@ class OverflowableToolbar {
+@@ -8030,11 +8033,11 @@ class OverflowableToolbar {
         parseFloat(style.paddingLeft) -
         parseFloat(style.paddingRight) -
         toolbarChildrenWidth;
@@ -185,7 +186,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
     });
 
     lazy.log.debug(
-@@ -7972,7 +7976,39 @@ class OverflowableToolbar {
+@@ -8049,7 +8052,39 @@ class OverflowableToolbar {
       Math.max(targetWidth, targetChildrenWidth)
     );
     totalAvailWidth = Math.ceil(totalAvailWidth);
@@ -226,7 +227,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
     return { isOverflowing, targetContentWidth, totalAvailWidth };
   }
 
-@@ -8033,7 +8069,11 @@ class OverflowableToolbar {
+@@ -8110,7 +8145,11 @@ class OverflowableToolbar {
             return;
           }
         }
@@ -239,7 +240,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
           lazy.log.debug(
             `Need ${minSize} but width is ${totalAvailWidth} so bailing`
           );
-@@ -8066,7 +8106,7 @@ class OverflowableToolbar {
+@@ -8143,7 +8182,7 @@ class OverflowableToolbar {
         }
       }
       if (!inserted) {
@@ -248,7 +249,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
       }
       child.removeAttribute("cui-anchorid");
       child.removeAttribute("overflowedItem");
-@@ -8192,6 +8232,9 @@ class OverflowableToolbar {
+@@ -8269,6 +8308,9 @@ class OverflowableToolbar {
    *   if no such list exists.
    */
   get #webExtList() {
@@ -258,7 +259,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
     if (!this.#webExtListRef) {
       let targetID = this.#toolbar.getAttribute("addon-webext-overflowtarget");
       if (!targetID) {
-@@ -8203,6 +8246,9 @@ class OverflowableToolbar {
+@@ -8280,6 +8322,9 @@ class OverflowableToolbar {
       let win = this.#toolbar.documentGlobal;
       let { panel } = win.gUnifiedExtensions;
       this.#webExtListRef = panel.querySelector(`#${targetID}`);
@@ -268,7 +269,7 @@ index 491161e48044f75167a8e8a0348779cfa22fc40e..867d51b8a6b74f841afc6d84dcdfd8f2
     }
     return this.#webExtListRef;
   }
-@@ -8411,7 +8457,7 @@ class OverflowableToolbar {
+@@ -8488,7 +8533,7 @@ class OverflowableToolbar {
         break;
       }
       case "mousedown": {
--- a/src/browser/components/preferences/preferences-js.patch
+++ b/src/browser/components/preferences/preferences-js.patch
@@ -1,8 +1,8 @@
 diff --git a/browser/components/preferences/preferences.js b/browser/components/preferences/preferences.js
-index c76a0647e14bac806d9428483bb565b3e10c31e7..2188f7808aca090f92574c7f5c55a28a9c5bb3f8 100644
+index a76699af75252bec31e17b562463c37236cbbfe5..6355a6ee92754846ffcdd123ac49545d520470c7 100644
 --- a/browser/components/preferences/preferences.js
 +++ b/browser/components/preferences/preferences.js
-@@ -131,6 +131,7 @@ ChromeUtils.defineLazyGetter(this, "gSubDialog", function () {
+@@ -132,6 +132,7 @@ ChromeUtils.defineLazyGetter(this, "gSubDialog", function () {
       styleSheets: [
         "chrome://browser/skin/preferences/dialog.css",
         "chrome://browser/skin/preferences/preferences.css",
@@ -10,7 +10,7 @@ index c76a0647e14bac806d9428483bb565b3e10c31e7..2188f7808aca090f92574c7f5c55a28a
       ],
       resizeCallback: async ({ title, frame }) => {
         // Search within main document and highlight matched keyword.
-@@ -437,6 +438,8 @@ const CONFIG_PANES = Object.freeze({
+@@ -462,6 +463,8 @@ const CONFIG_PANES = Object.freeze({
   tabsBrowsing: {
     l10nId: "tabs-browsing-section",
     groupIds: [
@@ -19,7 +19,7 @@ index c76a0647e14bac806d9428483bb565b3e10c31e7..2188f7808aca090f92574c7f5c55a28a
       "browserLayout",
       "tabs",
       "pageNavigation",
-@@ -483,7 +486,7 @@ function register_module(categoryName, categoryObject) {
+@@ -509,7 +512,7 @@ function register_module(categoryName, categoryObject) {
       }
       this._initted = true;
       let template = document.getElementById("template-" + categoryName);
@@ -28,7 +28,7 @@ index c76a0647e14bac806d9428483bb565b3e10c31e7..2188f7808aca090f92574c7f5c55a28a
         // Replace the template element with the nodes inside of it.
         template.replaceWith(template.content);
 
-@@ -527,6 +530,10 @@ function init_all() {
+@@ -553,6 +556,10 @@ function init_all() {
   register_module("paneHome", gHomePane);
   register_module("paneSearch", gSearchPane);
   register_module("panePrivacy", gPrivacyPane);
@@ -39,15 +39,3 @@ index c76a0647e14bac806d9428483bb565b3e10c31e7..2188f7808aca090f92574c7f5c55a28a
 
   // Restore the cached Firefox Labs nav button visibility so it shows
   // immediately when recipes are expected to be available, before
-@@ -656,9 +663,9 @@ async function gotoPref(
-   let redesignEnabled = srdSectionPrefs.all;
-   let categories = document.getElementById("categories");
-   const kDefaultCategoryInternalName = redesignEnabled
-    ? "paneSync"
-+    ? "paneTabsBrowsing"
-     : "paneGeneral";
-  const kDefaultCategory = redesignEnabled ? "sync" : "general";
-+  const kDefaultCategory = redesignEnabled ? "tabsBrowsing" : "general";
-   let hash = document.location.hash;
-   let category = aCategory || hash.substring(1) || kDefaultCategoryInternalName;
- 
--- a/src/browser/components/preferences/preferences-xhtml.patch
+++ b/src/browser/components/preferences/preferences-xhtml.patch
@@ -27,7 +27,7 @@ index 1b8c38159314b6edee9e6f455beb2b63db1ad3f0..1308345db640dba6b2848b49ef7c1181
 +      </html:moz-page-nav-button>
 +      <html:moz-page-nav-button id="category-zen-CKS"
 +        view="paneZenCKS"
-+        iconsrc="chrome://browser/skin/quickactions.svg"
+        iconsrc="chrome://browser/skin/preferences/category-accessibility.svg"
 +        data-l10n-id="pane-zen-CKS-title">
 +      </html:moz-page-nav-button>
 +      <html:moz-page-nav-button id="category-zen-marketplace"
--- a/src/browser/components/preferences/widgets/sync-engine-list/sync-engines-list-mjs.patch
+++ b/src/browser/components/preferences/widgets/sync-engine-list/sync-engines-list-mjs.patch
@@ -0,0 +1,15 @@
+diff --git a/browser/components/preferences/widgets/sync-engine-list/sync-engines-list.mjs b/browser/components/preferences/widgets/sync-engine-list/sync-engines-list.mjs
+index 9359a485ed6212c7df49a8d4b1e4a8febbc1c9b6..132fea440cfa535e78b35f706e7ef2d6881f9ba6 100644
+--- a/browser/components/preferences/widgets/sync-engine-list/sync-engines-list.mjs
+++ b/browser/components/preferences/widgets/sync-engine-list/sync-engines-list.mjs
+@@ -50,6 +50,10 @@ const engineTypeToMetadata = {
+     iconSrc: "chrome://global/skin/icons/settings.svg",
+     l10nId: "sync-currently-syncing-settings",
+   },
+  workspaces: {
+    iconSrc: "chrome://devtools/skin/images/tool-storage.svg",
+    l10nId: "sync-currently-syncing-workspaces",
+  },
+ };
+ 
+ /**
--- a/src/browser/components/sessionstore/SessionStore-sys-mjs.patch
+++ b/src/browser/components/sessionstore/SessionStore-sys-mjs.patch
@@ -1,18 +1,20 @@
 diff --git a/browser/components/sessionstore/SessionStore.sys.mjs b/browser/components/sessionstore/SessionStore.sys.mjs
-index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee4aa3be28 100644
+index 536e06eec9f35bad3b8366733b23b5a8697df9c8..631a16bc7518108641993836f0c52e2ab6e6c967 100644
 --- a/browser/components/sessionstore/SessionStore.sys.mjs
 +++ b/browser/components/sessionstore/SessionStore.sys.mjs
-@@ -129,6 +129,9 @@ const TAB_EVENTS = [
+@@ -129,6 +129,11 @@ const TAB_EVENTS = [
   "TabSplitViewActivate",
   "SplitViewRemoved",
   "SplitViewCreated",
 +  "TabAddedToEssentials",
 +  "TabRemovedFromEssentials",
+  "TabMove",
+  "TabGroupMoved",
 +  "ZenWorkspaceDataChanged",
 ];
 
 const XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
-@@ -201,6 +204,8 @@ ChromeUtils.defineESModuleGetters(lazy, {
+@@ -201,6 +206,8 @@ ChromeUtils.defineESModuleGetters(lazy, {
   TabStateCache: "resource:///modules/sessionstore/TabStateCache.sys.mjs",
   TabStateFlusher: "resource:///modules/sessionstore/TabStateFlusher.sys.mjs",
   setTimeout: "resource://gre/modules/Timer.sys.mjs",
@@ -21,7 +23,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 });
 
 ChromeUtils.defineLazyGetter(lazy, "blankURI", () => {
-@@ -1300,10 +1305,7 @@ var SessionStoreInternal = {
+@@ -1317,10 +1324,7 @@ var SessionStoreInternal = {
    */
   get willAutoRestore() {
     return (
@@ -33,17 +35,19 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
     );
   },
 
-@@ -1990,6 +1992,9 @@ var SessionStoreInternal = {
+@@ -2008,6 +2012,11 @@ var SessionStoreInternal = {
       case "TabPinned":
       case "TabUnpinned":
       case "SwapDocShells":
 +      case "TabRemovedFromEssentials":
 +      case "TabAddedToEssentials":
+      case "TabMove":
+      case "TabGroupMoved":
 +      case "ZenWorkspaceDataChanged":
         this.saveStateDelayed(win);
         break;
       case "TabGroupCreate":
-@@ -2099,6 +2104,10 @@ var SessionStoreInternal = {
+@@ -2117,6 +2126,10 @@ var SessionStoreInternal = {
       this._windows[aWindow.__SSi].isTaskbarTab = true;
     }
 
@@ -54,7 +58,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
     if (lazy.AIWindow.isAIWindowActiveAndEnabled(aWindow)) {
       this._windows[aWindow.__SSi].isAIWindow = true;
     }
-@@ -2135,7 +2144,7 @@ var SessionStoreInternal = {
+@@ -2153,7 +2166,7 @@ var SessionStoreInternal = {
     let isTaskbarTab = this._windows[aWindow.__SSi].isTaskbarTab;
     // A regular window is not a private window, taskbar tab window, or popup window
     let isRegularWindow =
@@ -63,7 +67,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 
     // perform additional initialization when the first window is loading
     if (lazy.RunState.isStopped) {
-@@ -2147,7 +2156,7 @@ var SessionStoreInternal = {
+@@ -2165,7 +2178,7 @@ var SessionStoreInternal = {
         // to disk to NOW() to enforce a full interval before the next write.
         lazy.SessionSaver.updateLastSaveTime();
 
@@ -72,7 +76,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
           this._log.debug(
             "initializeWindow, the window is private or a web app. Saving SessionStartup.state for possibly restoring later"
           );
-@@ -2191,6 +2200,7 @@ var SessionStoreInternal = {
+@@ -2209,6 +2222,7 @@ var SessionStoreInternal = {
           null,
           "sessionstore-one-or-no-tab-restored"
         );
@@ -80,7 +84,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
         this._deferredAllWindowsRestored.resolve();
       }
       // this window was opened by _openWindowWithState
-@@ -2240,7 +2250,6 @@ var SessionStoreInternal = {
+@@ -2258,7 +2272,6 @@ var SessionStoreInternal = {
       if (closedWindowState) {
         let newWindowState;
         if (
@@ -88,7 +92,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
           !lazy.SessionStartup.willRestore()
         ) {
           // We want to split the window up into pinned tabs and unpinned tabs.
-@@ -2276,6 +2285,7 @@ var SessionStoreInternal = {
+@@ -2294,6 +2307,7 @@ var SessionStoreInternal = {
         }
 
         if (newWindowState) {
@@ -96,7 +100,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
           // Ensure that the window state isn't hidden
           this._restoreCount = 1;
           let state = { windows: [newWindowState] };
-@@ -2312,6 +2322,9 @@ var SessionStoreInternal = {
+@@ -2330,6 +2344,9 @@ var SessionStoreInternal = {
       });
       this._shouldRestoreLastSession = false;
     }
@@ -106,7 +110,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 
     if (this._restoreLastWindow && aWindow.toolbar.visible) {
       // always reset (if not a popup window)
-@@ -2462,7 +2475,7 @@ var SessionStoreInternal = {
+@@ -2480,7 +2497,7 @@ var SessionStoreInternal = {
 
     var tabbrowser = aWindow.gBrowser;
 
@@ -115,7 +119,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 
     TAB_EVENTS.forEach(function (aEvent) {
       tabbrowser.tabContainer.removeEventListener(aEvent, this, true);
-@@ -2513,7 +2526,7 @@ var SessionStoreInternal = {
+@@ -2531,7 +2548,7 @@ var SessionStoreInternal = {
 
       let isLastRegularWindow =
         Object.values(this._windows).filter(
@@ -124,7 +128,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
         ).length == 1;
       this._log.debug(
         `onClose, closing window isLastRegularWindow? ${isLastRegularWindow}`
-@@ -2570,8 +2583,8 @@ var SessionStoreInternal = {
+@@ -2588,8 +2605,8 @@ var SessionStoreInternal = {
       // 2) Flush the window.
       // 3) When the flush is complete, revisit our decision to store the window
       //    in _closedWindows, and add/remove as necessary.
@@ -135,7 +139,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
       }
 
       completionPromise = lazy.TabStateFlusher.flushWindow(aWindow).then(() => {
-@@ -2591,8 +2604,9 @@ var SessionStoreInternal = {
+@@ -2609,8 +2626,9 @@ var SessionStoreInternal = {
 
         // Save non-private windows if they have at
         // least one saveable tab or are the last window.
@@ -147,7 +151,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 
           if (!isLastWindow && winData.closedId > -1) {
             this._addClosedAction(
-@@ -2668,7 +2682,7 @@ var SessionStoreInternal = {
+@@ -2686,7 +2704,7 @@ var SessionStoreInternal = {
    *        to call this method again asynchronously (for example, after
    *        a window flush).
    */
@@ -156,7 +160,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
     // Make sure SessionStore is still running, and make sure that we
     // haven't chosen to forget this window.
     if (
-@@ -2685,6 +2699,7 @@ var SessionStoreInternal = {
+@@ -2703,6 +2721,7 @@ var SessionStoreInternal = {
       // _closedWindows from a previous call to this function.
       let winIndex = this._closedWindows.indexOf(winData);
       let alreadyStored = winIndex != -1;
@@ -164,7 +168,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
       // If sidebar command is truthy, i.e. sidebar is open, store sidebar settings
       let shouldStore = hasSaveableTabs || isLastWindow;
 
-@@ -3507,7 +3522,7 @@ var SessionStoreInternal = {
+@@ -3525,7 +3544,7 @@ var SessionStoreInternal = {
     if (!isPrivateWindow && tabState.isPrivate) {
       return;
     }
@@ -173,7 +177,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
       return;
     }
 
-@@ -4246,6 +4261,12 @@ var SessionStoreInternal = {
+@@ -4264,6 +4283,12 @@ var SessionStoreInternal = {
         Math.min(tabState.index, tabState.entries.length)
       );
       tabState.pinned = false;
@@ -186,7 +190,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 
       if (inBackground === false) {
         aWindow.gBrowser.selectedTab = newTab;
-@@ -4679,6 +4700,8 @@ var SessionStoreInternal = {
+@@ -4697,6 +4722,8 @@ var SessionStoreInternal = {
       // Append the tab if we're opening into a different window,
       tabIndex: aSource == aTargetWindow ? pos : Infinity,
       pinned: state.pinned,
@@ -195,7 +199,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
       userContextId: state.userContextId,
       skipLoad: true,
       preferredRemoteType,
-@@ -5176,9 +5199,10 @@ var SessionStoreInternal = {
+@@ -5194,9 +5221,10 @@ var SessionStoreInternal = {
       if (activePageData.title && activePageData.title != activePageData.url) {
         win.gBrowser.setInitialTabTitle(tab, activePageData.title, {
           isContentTitle: true,
@@ -207,7 +211,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
       }
     }
 
-@@ -5543,7 +5567,7 @@ var SessionStoreInternal = {
+@@ -5561,7 +5589,7 @@ var SessionStoreInternal = {
 
     for (let i = tabbrowser.pinnedTabCount; i < tabbrowser.tabs.length; i++) {
       let tab = tabbrowser.tabs[i];
@@ -216,7 +220,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
         removableTabs.push(tab);
       }
     }
-@@ -5656,7 +5680,7 @@ var SessionStoreInternal = {
+@@ -5674,7 +5702,7 @@ var SessionStoreInternal = {
 
     // collect the data for all windows
     for (ix in this._windows) {
@@ -225,7 +229,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
         // window data is still in _statesToRestore
         continue;
       }
-@@ -5800,11 +5824,12 @@ var SessionStoreInternal = {
+@@ -5818,11 +5846,12 @@ var SessionStoreInternal = {
     }
 
     let tabbrowser = aWindow.gBrowser;
@@ -239,7 +243,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
     // update the internal state data for this window
     for (let tab of tabs) {
       if (tab == aWindow.FirefoxViewHandler.tab) {
-@@ -5815,6 +5840,9 @@ var SessionStoreInternal = {
+@@ -5833,6 +5862,9 @@ var SessionStoreInternal = {
       tabsData.push(tabData);
     }
 
@@ -249,7 +253,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
     // update tab group state for this window
     winData.groups = [];
     for (let tabGroup of aWindow.gBrowser.tabGroups) {
-@@ -5831,7 +5859,7 @@ var SessionStoreInternal = {
+@@ -5849,7 +5881,7 @@ var SessionStoreInternal = {
     // a window is closed, point to the first item in the tab strip instead (it will never be the Firefox View tab,
     // since it's only inserted into the tab strip after it's selected).
     if (aWindow.FirefoxViewHandler.tab?.selected) {
@@ -258,7 +262,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
       winData.title = tabbrowser.tabs[0].label;
     }
     winData.selected = selectedIndex;
-@@ -6033,8 +6061,8 @@ var SessionStoreInternal = {
+@@ -6051,8 +6083,8 @@ var SessionStoreInternal = {
     // selectTab represents.
     let selectTab = 0;
     if (overwriteTabs) {
@@ -269,7 +273,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
       selectTab = Math.min(selectTab, winData.tabs.length);
     }
 
-@@ -6056,6 +6084,7 @@ var SessionStoreInternal = {
+@@ -6074,6 +6106,7 @@ var SessionStoreInternal = {
     if (overwriteTabs) {
       for (let i = tabbrowser.browsers.length - 1; i >= 0; i--) {
         if (!tabbrowser.tabs[i].selected) {
@@ -277,7 +281,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
           tabbrowser.removeTab(tabbrowser.tabs[i]);
         }
       }
-@@ -6090,6 +6119,12 @@ var SessionStoreInternal = {
+@@ -6108,6 +6141,12 @@ var SessionStoreInternal = {
         savedTabGroup => !openTabGroupIdsInWindow.has(savedTabGroup.id)
       );
     }
@@ -290,7 +294,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 
     // Move the originally open tabs to the end.
     if (initialTabs) {
-@@ -6656,6 +6691,25 @@ var SessionStoreInternal = {
+@@ -6674,6 +6713,25 @@ var SessionStoreInternal = {
 
     // Most of tabData has been restored, now continue with restoring
     // attributes that may trigger external events.
@@ -316,7 +320,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 
     if (tabData.pinned) {
       tabbrowser.pinTab(tab);
-@@ -6838,6 +6892,9 @@ var SessionStoreInternal = {
+@@ -6859,6 +6917,9 @@ var SessionStoreInternal = {
         aWindow.gURLBar.readOnly = false;
       }
     }
@@ -326,7 +330,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
 
     let promiseParts = Promise.withResolvers();
     aWindow.setTimeout(() => {
-@@ -7633,7 +7690,7 @@ var SessionStoreInternal = {
+@@ -7654,7 +7715,7 @@ var SessionStoreInternal = {
 
       let groupsToSave = new Map();
       for (let tIndex = 0; tIndex < window.tabs.length; ) {
@@ -335,7 +339,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
           // Adjust window.selected
           if (tIndex + 1 < window.selected) {
             window.selected -= 1;
-@@ -7648,7 +7705,7 @@ var SessionStoreInternal = {
+@@ -7669,7 +7730,7 @@ var SessionStoreInternal = {
           );
           // We don't want to increment tIndex here.
           continue;
@@ -344,7 +348,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
           // Convert any open groups into saved groups.
           let groupStateToSave = window.groups.find(
             groupState => groupState.id == window.tabs[tIndex].groupId
-@@ -8193,7 +8250,6 @@ var SessionStoreInternal = {
+@@ -8233,7 +8294,6 @@ var SessionStoreInternal = {
     timer.initWithCallback(
       function () {
         if (beats <= 0) {
@@ -352,7 +356,7 @@ index 11191a82a0f0dc6eee60f9de52a63bc6085c3981..f995c3b297c53aa6ee2219bfc09515ee
           Glean.sessionRestore.shutdownFlushAllOutcomes.timed_out.add(1);
           deferred.resolve();
         }
-@@ -8671,6 +8727,7 @@ var SessionStoreInternal = {
+@@ -8711,6 +8771,7 @@ var SessionStoreInternal = {
     if (
       !savedTabGroupState.tabs.length ||
       this.getSavedTabGroup(savedTabGroupState.id)
--- a/src/browser/components/tabbrowser/content/drag-and-drop-js.patch
+++ b/src/browser/components/tabbrowser/content/drag-and-drop-js.patch
@@ -1,5 +1,5 @@
 diff --git a/browser/components/tabbrowser/content/drag-and-drop.js b/browser/components/tabbrowser/content/drag-and-drop.js
-index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b15a030046 100644
+index 70b37f93c4e8ff4ad9a2452681e468d23914c1b5..dbf2d9c83dafbe0e0b4e6caf3835edc8edf9bcf4 100644
 --- a/browser/components/tabbrowser/content/drag-and-drop.js
 +++ b/browser/components/tabbrowser/content/drag-and-drop.js
@@ -35,6 +35,9 @@
@@ -12,7 +12,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
     if (isTab(element) || isSplitViewWrapper(element)) {
       return element;
     }
-@@ -118,6 +121,9 @@
+@@ -128,6 +131,9 @@
       }
 
       let draggedTab = event.dataTransfer.mozGetDataAt(TAB_DROP_TYPE, 0);
@@ -22,7 +22,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
       if (
         (dropEffect == "move" || dropEffect == "copy") &&
         document == draggedTab.ownerDocument &&
-@@ -138,6 +144,7 @@
+@@ -148,6 +154,7 @@
           !draggedTab.group.collapsed
         ) {
           draggedTab.group.collapsed = true;
@@ -30,7 +30,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
         }
 
         if (dropEffect == "move") {
-@@ -145,10 +152,6 @@
+@@ -155,10 +162,6 @@
 
           // Pinned tabs in expanded vertical mode are on a grid format and require
           // different logic to drag and drop.
@@ -41,7 +41,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
           this._animateTabMove(event);
           return;
         }
-@@ -287,6 +290,10 @@
+@@ -297,6 +300,10 @@
 
       this._tabDropIndicator.hidden = true;
       event.stopPropagation();
@@ -52,7 +52,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
       if (draggedTab && dropEffect == "copy") {
         let duplicatedDraggedTab;
         let duplicatedTabs = [];
-@@ -312,12 +319,16 @@
+@@ -324,12 +331,16 @@
         let translateOffsetY = oldTranslateY % tabHeight;
         let newTranslateX = oldTranslateX - translateOffsetX;
         let newTranslateY = oldTranslateY - translateOffsetY;
@@ -73,7 +73,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
 
         if (this._tabbrowserTabs.isContainerVerticalPinnedGrid(draggedTab)) {
           // Update both translate axis for pinned vertical expanded tabs
-@@ -392,11 +403,13 @@
+@@ -404,11 +415,13 @@
           this._dragToPinPromoCard,
         ];
         let shouldPin =
@@ -87,15 +87,15 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
           isTab(draggedTab) &&
           draggedTab.pinned &&
           this._tabbrowserTabs.arrowScrollbox.contains(event.target);
-@@ -466,6 +479,7 @@
+@@ -484,6 +497,7 @@
           }
         }
 
 +        shouldTranslate = false;
         if (shouldTranslate) {
+           this.#dropAnimationEndTime = Date.now() + DROP_ANIMATION_GRACE_MS;
           let translationPromises = [];
-           for (let item of movingTabs) {
-@@ -477,7 +491,7 @@
+@@ -496,7 +510,7 @@
                 item.removeAttribute("tabdrop-samewindow");
                 resolve();
               };
@@ -104,7 +104,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
                 postTransitionCleanup();
               } else {
                 let onTransitionEnd = transitionendEvent => {
-@@ -552,7 +566,7 @@
+@@ -580,7 +594,7 @@
           if (tab.selected) {
             selectedTab = tab;
             indexForSelectedTab = newIndex;
@@ -113,7 +113,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
             const droppedIntoPinnedArea = dropIndex < gBrowser.pinnedTabCount;
             const newSplitView = gBrowser.adoptSplitView(tab, {
               elementIndex: droppedIntoPinnedArea
-@@ -577,7 +591,7 @@
+@@ -605,7 +619,7 @@
             }
           }
         }
@@ -122,7 +122,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
           const newTab = gBrowser.adoptTab(selectedTab, {
             elementIndex: indexForSelectedTab,
             selectTab: selectedTab == draggedTab,
-@@ -611,10 +625,6 @@
+@@ -639,10 +653,6 @@
               this._tabbrowserTabs.dragAndDropElements[
                 gBrowser.pinnedTabCount + unpinnedSplitViews.length - 1
               ];
@@ -133,7 +133,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
           }
         }
       } else {
-@@ -664,6 +674,7 @@
+@@ -703,6 +713,7 @@
 
           let nextItem = this._tabbrowserTabs.dragAndDropElements[newIndex];
           let tabGroup = isTab(nextItem) && nextItem.group;
@@ -141,12 +141,15 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
           gBrowser.loadTabs(urls, {
             inBackground,
             replace,
-@@ -705,7 +716,16 @@
+@@ -744,6 +755,22 @@
         this._expandGroupOnDrop(draggedTab);
       }
-       this._resetTabsAfterDrop(draggedTab.ownerDocument);
-
-+      if (!dt.mozUserCancelled && dt.dropEffect == "none" && !this._isCustomizing) {
+       this._resetTabsAfterDrop(draggedTab);
+      if (
+        !dt.mozUserCancelled &&
+        dt.dropEffect == "none" &&
+        !this._tabbrowserTabs._isCustomizing
+      ) {
 +        const moved = gZenViewSplitter.moveTabToSplitView(event, draggedTab);
 +        if (moved) {
 +          delete draggedTab._dragData;
@@ -154,12 +157,14 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
 +        }
 +      } else if (dt.mozUserCancelled) {
 +        gZenViewSplitter.onBrowserDragEndToSplit(event, true);
-+        if (gZenViewSplitter._lastOpenedTab) gZenViewSplitter._lastOpenedTab._visuallySelected = false;
+        if (gZenViewSplitter._lastOpenedTab) {
+          gZenViewSplitter._lastOpenedTab._visuallySelected = false;
+        }
 +      }
+ 
       if (
         dt.mozUserCancelled ||
-         dt.dropEffect != "none" ||
-@@ -927,11 +947,10 @@
+@@ -1074,11 +1101,10 @@
         return this.#getHorizontalScrollboxDragTarget(event, ignoreSides);
       }
       while (target) {
@@ -175,7 +180,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
           break;
         }
         target = target.parentNode;
-@@ -961,6 +980,9 @@
+@@ -1108,6 +1134,9 @@
           return null;
         }
       }
@@ -185,17 +190,36 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
       return target;
     }
 
-@@ -1014,7 +1036,8 @@
-         isTabGroupLabel(draggedTab) &&
-         draggedTab._dragData?.expandGroupOnDrop
-       ) {
-        draggedTab.group.collapsed = false;
-+        draggedTab.group.collapsed = draggedTab.group.hasAttribute("has-active");
-+        gZenFolders.animateGroupMove(draggedTab.group, true);
+@@ -1170,14 +1199,20 @@
+       let releaseReservedSpace = () =>
+         this.#releaseSpaceInScrolledContent(periphery);
+       if (group.collapsed) {
+-        // The group's tabs animate back to their full size, so hold on to the
+-        // space reserved for them until they get there.
+-        group.addEventListener(
+-          "TabGroupAnimationComplete",
+-          releaseReservedSpace,
+-          { once: true }
+-        );
+-        group.collapsed = false;
+        const expand = !group.hasAttribute("has-active");
+        if (expand) {
+          // The group's tabs animate back to their full size, so hold on to the
+          // space reserved for them until they get there.
+          group.addEventListener(
+            "TabGroupAnimationComplete",
+            releaseReservedSpace,
+            { once: true }
+          );
+        } else {
+          releaseReservedSpace();
+        }
+        group.collapsed = !expand;
+        gZenFolders.animateGroupMove(group, true);
+       } else {
+         releaseReservedSpace();
       }
-     }
- 
-@@ -1206,7 +1229,6 @@
+@@ -1362,7 +1397,6 @@
         // using updateDragImage. On Linux, we can use a panel.
         if (platform == "win" || platform == "macosx") {
           captureListener = function () {
@@ -203,7 +227,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
           };
         } else {
           // Create a panel to use it in setDragImage
-@@ -1244,7 +1266,6 @@
+@@ -1400,7 +1434,6 @@
         );
         dragImageOffset = dragImageOffset * scale;
       }
@@ -211,7 +235,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
 
       // _dragData.offsetX/Y give the coordinates that the mouse should be
       // positioned relative to the corner of the new window created upon
-@@ -1263,7 +1284,7 @@
+@@ -1419,7 +1452,7 @@
       let dropEffect = this.getDropEffectForTabDrag(event);
       let isMovingInTabStrip = !fromTabList && dropEffect == "move";
       let collapseTabGroupDuringDrag =
@@ -220,7 +244,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
 
       tab._dragData = {
         offsetX: this._tabbrowserTabs.verticalMode
-@@ -1273,7 +1294,7 @@
+@@ -1429,7 +1462,7 @@
           ? event.screenY - window.screenY - tabOffset
           : event.screenY - window.screenY,
         scrollPos:
@@ -229,7 +253,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
             ? this._tabbrowserTabs.pinnedTabsContainer.scrollPosition
             : this._tabbrowserTabs.arrowScrollbox.scrollPosition,
         screenX: event.screenX,
-@@ -1320,6 +1341,7 @@
+@@ -1522,6 +1555,7 @@
       if (tabStripItemElement.hasAttribute("dragtarget")) {
         return;
       }
@@ -237,7 +261,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
       let isPinned = tab.pinned;
       let dragAndDropElements = this._tabbrowserTabs.dragAndDropElements;
       let isGrid = this._tabbrowserTabs.isContainerVerticalPinnedGrid(tab);
-@@ -1686,23 +1708,6 @@
+@@ -1895,23 +1929,6 @@
 
       // Slide the relevant tabs to their new position.
       // non-moving tabs adjust for RTL
@@ -261,7 +285,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
       // moving tabs don't adjust for RTL
       for (let item of selectedElements) {
         if (
-@@ -1751,7 +1756,6 @@
+@@ -1960,7 +1977,6 @@
       for (let item of this._tabbrowserTabs.dragAndDropElements) {
         delete item._moveTogetherSelectedTabsData;
         item = elementToMove(item);
@@ -269,7 +293,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
         item.removeAttribute("multiselected-move-together");
       }
     }
-@@ -2598,7 +2602,6 @@
+@@ -2812,7 +2828,6 @@
         tab.style.top = "";
         tab.style.maxWidth = "";
         tab.style.pointerEvents = "";
@@ -277,7 +301,7 @@ index 8bb1219962a1368f50b53c61041f135c68e35f31..8e72441d26883cbef7a352b00c0fe2b1
         tab.removeAttribute("small-stack");
         tab.removeAttribute("big-stack");
       }
-@@ -2607,11 +2610,9 @@
+@@ -2821,11 +2836,9 @@
       )) {
         label.style.width = "";
         label.style.maxWidth = "";
--- a/src/browser/components/tabbrowser/content/tab-context-menu-js.patch
+++ b/src/browser/components/tabbrowser/content/tab-context-menu-js.patch
@@ -1,8 +1,8 @@
 diff --git a/browser/components/tabbrowser/content/tab-context-menu.js b/browser/components/tabbrowser/content/tab-context-menu.js
-index 4a7cb33a4d9067d469bbe09d4cd8844581642f7a..2e2404b78deb428e57d01b8b929231f675a21323 100644
+index 4a7cb33a4d9067d469bbe09d4cd8844581642f7a..d7f75471a207cccac6ca3dec49037ac30dd76163 100644
 --- a/browser/components/tabbrowser/content/tab-context-menu.js
 +++ b/browser/components/tabbrowser/content/tab-context-menu.js
-@@ -839,7 +839,8 @@ var TabContextMenu = {
+@@ -839,13 +839,15 @@ var TabContextMenu = {
     );
     contextUnpinSelectedTabs.hidden =
       !this.contextTab.pinned || !this.multiselected;
@@ -12,3 +12,10 @@ index 4a7cb33a4d9067d469bbe09d4cd8844581642f7a..2e2404b78deb428e57d01b8b929231f6
     // Build Ask Chat items. The classic layout shows the full ask-chat submenu
     // (#context_askChat); the alt layout shows only a flat "Summarize Page" item
     // (#context_askChatSummarize). Hide whichever one this layout doesn't use so
+     // a pref toggle reverses cleanly.
+     if (!this._altTabContextMenu) {
+       document.getElementById("context_askChatSummarize").hidden = true;
+      document.getElementById("context_aiSeparator").hidden = true;
+       TabContextMenu.GenAI.buildTabMenu(
+         document.getElementById("context_askChat"),
+         this
--- a/src/browser/components/tabbrowser/content/tabbrowser-js.patch
+++ b/src/browser/components/tabbrowser/content/tabbrowser-js.patch
@@ -1,8 +1,8 @@
 diff --git a/browser/components/tabbrowser/content/tabbrowser.js b/browser/components/tabbrowser/content/tabbrowser.js
-index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da5504f9d8 100644
+index 43180487a2fac15b7a65fac94f233eeed9094990..ae1288974cae29da929f27b78ff8db542566eba2 100644
 --- a/browser/components/tabbrowser/content/tabbrowser.js
 +++ b/browser/components/tabbrowser/content/tabbrowser.js
-@@ -513,6 +513,7 @@
+@@ -514,6 +514,7 @@
      * @type {MozBrowser[]}
      */
     get splitViewBrowsers() {
@@ -10,7 +10,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       const browsers = [];
       if (this.#activeSplitView) {
         for (const tab of this.#activeSplitView.tabs) {
-@@ -611,15 +612,66 @@
+@@ -612,15 +613,66 @@
       return this.tabContainer.visibleTabs;
     }
 
@@ -79,7 +79,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
     setSelectedTab(val, metricsContext = null) {
       if (this.selectedTab === val) {
         return;
-@@ -632,6 +684,9 @@
+@@ -633,6 +685,9 @@
       ) {
         return;
       }
@@ -89,7 +89,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       // Update the tab
       this.tabbox.selectedTab = val;
 
-@@ -708,6 +763,10 @@
+@@ -709,6 +764,10 @@
         userContextId = parseInt(tabArgument.getAttribute("usercontextid"), 10);
       }
 
@@ -100,7 +100,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       if (openWindowInfo) {
         userContextId = openWindowInfo.originAttributes.userContextId;
       }
-@@ -809,6 +868,8 @@
+@@ -810,6 +869,8 @@
       this.tabpanels.appendChild(panel);
 
       let tab = this.tabs[0];
@@ -109,7 +109,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       tab.linkedPanel = uniqueId;
       this._selectedTab = tab;
       this._selectedBrowser = browser;
-@@ -1178,18 +1239,24 @@
+@@ -1179,18 +1240,24 @@
      *   The context for the operation for telemetry purposes, defaults to an unknown context.
      */
     pinTab(aTab, { metricsContext = this.TabMetrics.UNKNOWN_CONTEXT } = {}) {
@@ -135,7 +135,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       aTab.setAttribute("pinned", "true");
       this._updateTabBarForPinnedTabs();
-@@ -1206,16 +1273,25 @@
+@@ -1207,16 +1274,25 @@
      *   The context for the operation for telemetry purposes, defaults to an unknown context.
      */
     unpinTab(aTab, { metricsContext = this.TabMetrics.UNKNOWN_CONTEXT } = {}) {
@@ -162,7 +162,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       });
 
       aTab.style.marginInlineStart = "";
-@@ -1430,6 +1506,9 @@
+@@ -1432,6 +1508,9 @@
 
       let LOCAL_PROTOCOLS = ["chrome:", "about:", "resource:", "data:"];
 
@@ -172,7 +172,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       if (
         aIconURL &&
         !LOCAL_PROTOCOLS.some(protocol => aIconURL.startsWith(protocol))
-@@ -1439,6 +1518,9 @@
+@@ -1441,6 +1520,9 @@
         );
         return;
       }
@@ -182,7 +182,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       let browser = this.getBrowserForTab(aTab);
       browser.mIconURL = aIconURL;
-@@ -1761,7 +1843,6 @@
+@@ -1763,7 +1845,6 @@
 
       // Preview mode should not reset the owner
       if (!this.#previewMode && !oldTab.selected) {
@@ -190,7 +190,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       }
 
       let lastRelatedTab = this.#lastRelatedTabMap.get(oldTab);
-@@ -1852,6 +1933,7 @@
+@@ -1854,6 +1935,7 @@
       if (!this.#previewMode) {
         newTab.recordTimeFromUnloadToReload();
         newTab.updateLastAccessed();
@@ -198,7 +198,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         oldTab.updateLastAccessed();
         // if this is the foreground window, update the last-seen timestamps.
         if (this.documentGlobal == BrowserWindowTracker.getTopWindow()) {
-@@ -2066,6 +2148,9 @@
+@@ -2068,6 +2150,9 @@
       }
 
       let activeEl = document.activeElement;
@@ -208,7 +208,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       // If focus is on the old tab, move it to the new tab.
       if (activeEl == oldTab) {
         newTab.focus();
-@@ -2104,7 +2189,7 @@
+@@ -2106,7 +2191,7 @@
       // Focus the location bar if it was previously focused for that tab.
       // In full screen mode, only bother making the location bar visible
       // if the tab is a blank one.
@@ -217,7 +217,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         let selectURL = () => {
           if (this._asyncTabSwitching) {
             // Set _awaitingSetURI flag to suppress popup notification
-@@ -2392,7 +2477,12 @@
+@@ -2394,7 +2479,12 @@
       return this._setTabLabel(aTab, aLabel);
     }
 
@@ -231,7 +231,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       if (!aLabel || (isURL && /^about:reader\?url=/.test(aLabel))) {
         return false;
       }
-@@ -2518,7 +2608,7 @@
+@@ -2520,7 +2610,7 @@
         newIndex = this.selectedTab._tPos + 1;
       }
 
@@ -240,7 +240,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         if (this.isTabGroupLabel(targetTab)) {
           throw new Error(
             "Replacing a tab group label with a tab is not supported"
-@@ -2793,6 +2883,7 @@
+@@ -2795,6 +2885,7 @@
       uriIsAboutBlank,
       userContextId,
       skipLoad,
@@ -248,7 +248,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
     } = {}) {
       let b = document.createXULElement("browser");
       // Use the JSM global to create the permanentKey, so that if the
-@@ -2866,8 +2957,7 @@
+@@ -2868,8 +2959,7 @@
         // we use a different attribute name for this?
         b.setAttribute("name", name);
       }
@@ -258,7 +258,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         b.setAttribute("transparent", "true");
       }
 
-@@ -3022,7 +3112,7 @@
+@@ -3024,7 +3114,7 @@
 
       let panel = this.getPanel(browser);
       let uniqueId = this._generateUniquePanelID();
@@ -267,7 +267,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       aTab.linkedPanel = uniqueId;
 
       // Inject the <browser> into the DOM if necessary.
-@@ -3082,8 +3172,8 @@
+@@ -3084,8 +3174,8 @@
       // If we transitioned from one browser to two browsers, we need to set
       // hasSiblings=false on both the existing browser and the new browser.
       if (this.tabs.length == 2) {
@@ -278,7 +278,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       } else {
         aTab.linkedBrowser.browsingContext.hasSiblings = this.tabs.length > 1;
       }
-@@ -3268,7 +3358,6 @@
+@@ -3270,7 +3360,6 @@
             this.selectedTab = this.addTrustedTab(BROWSER_NEW_TAB_URL, {
               tabIndex: tab._tPos + 1,
               userContextId: tab.userContextId,
@@ -286,7 +286,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
               focusUrlBar: true,
             });
             resolve(this.selectedBrowser);
-@@ -3378,6 +3467,10 @@
+@@ -3380,6 +3469,10 @@
         schemelessInput,
         hasValidUserGestureActivation = false,
         textDirectiveUserActivation = false,
@@ -297,7 +297,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       } = {}
     ) {
       // all callers of addTab that pass a params object need to pass
-@@ -3388,10 +3481,25 @@
+@@ -3390,10 +3483,25 @@
         );
       }
 
@@ -323,7 +323,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       // If we're opening a foreground tab, set the owner by default.
       ownerTab ??= inBackground ? null : this.selectedTab;
 
-@@ -3399,6 +3507,7 @@
+@@ -3401,6 +3509,7 @@
       if (this.selectedTab.owner) {
         this.selectedTab.owner = null;
       }
@@ -331,7 +331,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       // Find the tab that opened this one, if any. This is used for
       // determining positioning, and inherited attributes such as the
-@@ -3451,6 +3560,22 @@
+@@ -3453,6 +3562,22 @@
           noInitialLabel,
           skipBackgroundNotify,
         });
@@ -354,7 +354,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         if (insertTab) {
           // Insert the tab into the tab container in the correct position.
           this.#insertTabAtIndex(t, {
-@@ -3459,6 +3584,7 @@
+@@ -3461,6 +3586,7 @@
             ownerTab,
             openerTab,
             pinned,
@@ -362,7 +362,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
             bulkOrderedOpen,
             tabGroup: tabGroup ?? openerTab?.group,
           });
-@@ -3477,6 +3603,7 @@
+@@ -3479,6 +3605,7 @@
           openWindowInfo,
           skipLoad,
           triggeringRemoteType,
@@ -370,7 +370,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         }));
 
         if (focusUrlBar) {
-@@ -3601,6 +3728,12 @@
+@@ -3603,6 +3730,12 @@
         }
       }
 
@@ -383,7 +383,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       // Additionally send pinned tab events
       if (pinned) {
         this.#notifyPinnedStatus(t);
-@@ -3611,6 +3744,15 @@
+@@ -3613,6 +3746,15 @@
       if (!inBackground) {
         this.selectedTab = t;
       }
@@ -399,7 +399,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       return t;
     }
 
-@@ -3834,6 +3976,7 @@
+@@ -3836,6 +3978,7 @@
         insertBefore = null,
         isAdoptingGroup = false,
         metricsContext = this.TabMetrics.UNKNOWN_CONTEXT,
@@ -407,7 +407,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       } = {}
     ) {
       if (
-@@ -3844,9 +3987,6 @@
+@@ -3846,9 +3989,6 @@
             !this.isSplitViewWrapper(tabOrSplitView)
         )
       ) {
@@ -417,7 +417,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       }
 
       if (!color) {
-@@ -3867,9 +4007,14 @@
+@@ -3869,9 +4009,14 @@
         label,
         isAdoptingGroup
       );
@@ -434,7 +434,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       );
       group.addTabs(tabsAndSplitViews, metricsContext);
 
-@@ -3973,7 +4118,7 @@
+@@ -3975,7 +4120,7 @@
       }
 
       this.#handleTabMove(tab, () =>
@@ -443,7 +443,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       );
     }
 
-@@ -4059,6 +4204,7 @@
+@@ -4061,6 +4206,7 @@
         color: group.color,
         insertBefore: newTabs[0],
         isAdoptingGroup: true,
@@ -451,7 +451,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       });
     }
 
-@@ -4269,6 +4415,7 @@
+@@ -4271,6 +4417,7 @@
         openWindowInfo,
         skipLoad,
         triggeringRemoteType,
@@ -459,7 +459,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       }
     ) {
       // If we don't have a preferred remote type (or it is `NOT_REMOTE`), and
-@@ -4329,6 +4476,7 @@
+@@ -4331,6 +4478,7 @@
           openWindowInfo,
           name,
           skipLoad,
@@ -467,7 +467,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         });
       }
 
-@@ -4542,9 +4690,9 @@
+@@ -4544,9 +4692,9 @@
         }
 
         // Add a new tab if needed.
@@ -479,7 +479,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
           let url = "about:blank";
           if (tabData.entries?.length) {
-@@ -4577,8 +4725,10 @@
+@@ -4579,8 +4727,10 @@
             insertTab: false,
             skipLoad: true,
             preferredRemoteType,
@@ -491,7 +491,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
           if (select) {
             tabToSelect = tab;
           }
-@@ -4600,7 +4750,8 @@
+@@ -4602,7 +4752,8 @@
           this.pinTab(tab);
           // Then ensure all the tab open/pinning information is sent.
           this._fireTabOpen(tab, {});
@@ -501,7 +501,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
           let { groupId } = tabData;
           const tabGroup = tabGroupWorkingData.get(groupId);
           // if a tab refers to a tab group we don't know, skip any group
-@@ -4620,7 +4771,10 @@
+@@ -4622,7 +4773,10 @@
                 tabGroup.stateData.id,
                 tabGroup.stateData.color,
                 tabGroup.stateData.collapsed,
@@ -513,7 +513,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
               );
               tabsFragment.appendChild(tabGroup.node);
             }
-@@ -4675,9 +4829,21 @@
+@@ -4677,9 +4831,21 @@
       // to remove the old selected tab.
       if (tabToSelect) {
         let leftoverTab = this.selectedTab;
@@ -535,7 +535,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       if (tabs.length > 1 || !tabs[0].selected) {
         this._updateTabsAfterInsert();
-@@ -4882,11 +5048,17 @@
+@@ -4884,11 +5050,17 @@
       if (ownerTab) {
         tab.owner = ownerTab;
       }
@@ -554,7 +554,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         if (
           !bulkOrderedOpen &&
           ((openerTab &&
-@@ -4898,7 +5070,7 @@
+@@ -4900,7 +5072,7 @@
           let lastRelatedTab =
             openerTab && this.#lastRelatedTabMap.get(openerTab);
           let previousTab = lastRelatedTab || openerTab || this.selectedTab;
@@ -563,7 +563,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
             tabGroup = previousTab.group;
           }
           if (
-@@ -4914,7 +5086,7 @@
+@@ -4916,7 +5088,7 @@
                 previousTab.splitview
               ) + 1;
           } else if (previousTab.visible) {
@@ -572,7 +572,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
           } else if (previousTab == FirefoxViewHandler.tab) {
             elementIndex = 0;
           }
-@@ -4942,14 +5114,14 @@
+@@ -4944,14 +5116,14 @@
       }
       // Ensure index is within bounds.
       if (tab.pinned) {
@@ -591,7 +591,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       if (pinned && !itemAfter?.pinned) {
         itemAfter = null;
-@@ -4966,7 +5138,7 @@
+@@ -4968,7 +5140,7 @@
 
       this.tabContainer._invalidateCachedTabs();
 
@@ -600,7 +600,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         if (
           (this.isTab(itemAfter) && itemAfter.group == tabGroup) ||
           this.isSplitViewWrapper(itemAfter)
-@@ -4997,7 +5169,11 @@
+@@ -4999,7 +5171,11 @@
         const tabContainer = pinned
           ? this.tabContainer.pinnedTabsContainer
           : this.tabContainer;
@@ -612,7 +612,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       }
 
       if (tab.group?.collapsed) {
-@@ -5012,6 +5188,7 @@
+@@ -5014,6 +5190,7 @@
       if (pinned) {
         this._updateTabBarForPinnedTabs();
       }
@@ -620,7 +620,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       TabBarVisibility.update();
     }
-@@ -5568,6 +5745,7 @@
+@@ -5577,6 +5754,7 @@
         metricsContext,
       } = {}
     ) {
@@ -628,7 +628,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       // When 'closeWindowWithLastTab' pref is enabled, closing all tabs
       // can be considered equivalent to closing the window.
       if (
-@@ -5678,6 +5856,7 @@
+@@ -5687,6 +5865,7 @@
             closedTabCount -= 1;
           }
         }
@@ -636,7 +636,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
         if (closedTabCount > 0) {
           this.recordTabMetrics(
-@@ -5730,6 +5909,14 @@
+@@ -5761,6 +5940,14 @@
         return;
       }
 
@@ -651,7 +651,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       let isVisibleTab = aTab.visible;
       // We have to sample the tab width now, since _beginRemoveTab might
       // end up modifying the DOM in such a way that aTab gets a new
-@@ -5737,6 +5924,9 @@
+@@ -5768,6 +5955,9 @@
       // state).
       let tabWidth = window.windowUtils.getBoundsWithoutFlushing(aTab).width;
       let isLastTab = this.#isLastTabInWindow(aTab);
@@ -661,7 +661,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       if (
         !this._beginRemoveTab(aTab, {
           closeWindowFastpath: true,
-@@ -5747,13 +5937,14 @@
+@@ -5778,13 +5968,14 @@
           metricsContext,
         })
       ) {
@@ -677,7 +677,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       let lockTabSizing =
         !this.tabContainer.verticalMode &&
         !aTab.pinned &&
-@@ -5784,7 +5975,13 @@
+@@ -5815,7 +6006,13 @@
         // We're not animating, so we can cancel the animation stopwatch.
         Glean.browserTabclose.timeAnim.cancel(aTab._closeTimeAnimTimerId);
         aTab._closeTimeAnimTimerId = null;
@@ -692,7 +692,18 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         return;
       }
 
-@@ -5827,7 +6024,7 @@
+@@ -5855,7 +6052,9 @@
+     get #shouldCloseWindowWithLastTab() {
+       return (
+         !window.toolbar.visible ||
+-        Services.prefs.getBoolPref("browser.tabs.closeWindowWithLastTab")
+        (Services.prefs.getBoolPref("browser.tabs.closeWindowWithLastTab") &&
+          !gZenWorkspaces._isClosingWindow &&
+          !gZenWorkspaces._removedByStartupPage)
+       );
+     }
+ 
+@@ -5871,7 +6070,7 @@
      */
     #isLastTabInWindow(tab) {
       for (const otherTab of this.tabs) {
@@ -701,16 +712,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
           return false;
         }
       }
-@@ -5917,7 +6114,7 @@
-           closeWindowWithLastTab != null
-             ? closeWindowWithLastTab
-             : !window.toolbar.visible ||
-              Services.prefs.getBoolPref("browser.tabs.closeWindowWithLastTab");
-+              Services.prefs.getBoolPref("browser.tabs.closeWindowWithLastTab") && !gZenWorkspaces._isClosingWindow && !gZenWorkspaces._removedByStartupPage;
- 
-         if (closeWindow) {
-           // We've already called beforeunload on all the relevant tabs if we get here,
-@@ -5941,6 +6138,7 @@
+@@ -5982,6 +6181,7 @@
 
         newTab = true;
       }
@@ -718,8 +720,8 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       aTab._endRemoveArgs = [closeWindow, newTab];
 
       // swapBrowsersAndCloseOther will take care of closing the window without animation.
-@@ -5982,13 +6180,7 @@
-       aTab._mouseleave();
+@@ -6029,13 +6229,7 @@
+       }
 
       if (newTab) {
 -        this.addTrustedTab(BROWSER_NEW_TAB_URL, {
@@ -733,7 +735,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       } else {
         TabBarVisibility.update();
       }
-@@ -6128,6 +6320,7 @@
+@@ -6192,6 +6386,7 @@
         this.tabs[i]._tPos = i;
       }
 
@@ -741,7 +743,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       if (!this.#windowIsClosing) {
         // update tab close buttons state
         this.tabContainer._updateCloseButtons();
-@@ -6313,6 +6506,7 @@
+@@ -6377,6 +6572,7 @@
         memory_after: await getTotalMemoryUsage(),
         time_to_unload_in_ms: timeElapsed,
       });
@@ -749,7 +751,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
     }
 
     /**
-@@ -6358,6 +6552,7 @@
+@@ -6422,6 +6618,7 @@
       }
 
       let excludeTabs = new Set(aExcludeTabs);
@@ -757,7 +759,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       // If this tab has a successor, it should be selectable, since
       // hiding or closing a tab removes that tab as a successor.
-@@ -6370,13 +6565,13 @@
+@@ -6434,13 +6631,13 @@
         !excludeTabs.has(aTab.owner) &&
         Services.prefs.getBoolPref("browser.tabs.selectOwnerOnClose")
       ) {
@@ -773,7 +775,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       );
 
       if (Services.prefs.getBoolPref("browser.tabs.selectMRUOnClose", false)) {
-@@ -6392,6 +6587,13 @@
+@@ -6456,6 +6653,13 @@
         }
       }
 
@@ -787,7 +789,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       let tab = this.tabContainer.findNextTab(aTab, {
         direction: 1,
         filter: _tab => remainingTabs.includes(_tab),
-@@ -6405,7 +6607,7 @@
+@@ -6469,7 +6673,7 @@
       }
 
       if (tab) {
@@ -796,7 +798,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       }
 
       // If no qualifying visible tab was found, see if there is a tab in
-@@ -6426,7 +6628,7 @@
+@@ -6490,7 +6694,7 @@
         });
       }
 
@@ -805,7 +807,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
     }
 
     _blurTab(aTab) {
-@@ -6437,7 +6639,7 @@
+@@ -6501,7 +6705,7 @@
      * @returns {boolean}
      *   False if swapping isn't permitted, true otherwise.
      */
@@ -814,7 +816,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       // Do not allow transfering a private tab to a non-private window
       // and vice versa.
       if (
-@@ -6491,6 +6693,7 @@
+@@ -6555,6 +6759,7 @@
       // fire the beforeunload event in the process.  Close the other
       // window if this was its last tab.
       if (
@@ -822,7 +824,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         !remoteBrowser._beginRemoveTab(aOtherTab, {
           adoptedByTab: aOurTab,
           closeWindowWithLastTab: true,
-@@ -6502,7 +6705,7 @@
+@@ -6566,7 +6771,7 @@
       // If this is the last tab of the window, hide the window
       // immediately without animation before the docshell swap, to avoid
       // about:blank being painted.
@@ -831,7 +833,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       if (closeWindow) {
         let win = aOtherTab.documentGlobal;
         win.windowUtils.suppressAnimation(true);
-@@ -6636,11 +6839,13 @@
+@@ -6700,11 +6905,13 @@
       }
 
       // Finish tearing down the tab that's going away.
@@ -845,7 +847,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       this.setTabTitle(aOurTab);
 
-@@ -6860,10 +7065,10 @@
+@@ -6928,10 +7135,10 @@
       SessionStore.deleteCustomTabValue(aTab, "hiddenBy");
     }
 
@@ -858,7 +860,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         aTab.selected ||
         aTab.closing ||
         // Tabs that are sharing the screen, microphone or camera cannot be hidden.
-@@ -6923,7 +7128,8 @@
+@@ -6991,7 +7198,8 @@
      * @param {object} [aOptions={}]
      *   Key-value pairs that will be serialized into the features string.
      */
@@ -868,7 +870,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       if (this.tabs.length == 1) {
         return null;
       }
-@@ -6940,7 +7146,7 @@
+@@ -7008,7 +7216,7 @@
       // tell a new window to take the "dropped" tab
       let args = Cc["@mozilla.org/array;1"].createInstance(Ci.nsIMutableArray);
       args.appendElement(aTab.splitview ?? aTab);
@@ -877,7 +879,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         private: PrivateBrowsingUtils.isWindowPrivate(window),
         features: Object.entries(aOptions)
           .map(([key, value]) => `${key}=${value}`)
-@@ -6948,6 +7154,8 @@
+@@ -7016,6 +7224,8 @@
         openerWindow: window,
         args,
       });
@@ -886,7 +888,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
     }
 
     /**
-@@ -7074,7 +7282,7 @@
+@@ -7142,7 +7352,7 @@
      *   `true` if element is a `<tab-group>`
      */
     isTabGroup(element) {
@@ -895,7 +897,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
     }
 
     /**
-@@ -7146,8 +7354,8 @@
+@@ -7214,8 +7424,8 @@
       }
 
       // Don't allow mixing pinned and unpinned tabs.
@@ -906,7 +908,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       } else {
         tabIndex = Math.max(tabIndex, this.pinnedTabCount);
       }
-@@ -7193,8 +7401,8 @@
+@@ -7261,8 +7471,8 @@
       this.#handleTabMove(
         element,
         () => {
@@ -917,7 +919,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
             neighbor = neighbor.group;
           }
           if (neighbor?.splitview) {
-@@ -7205,6 +7413,12 @@
+@@ -7273,6 +7483,12 @@
               return;
             }
           }
@@ -930,7 +932,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
           if (movingForwards && neighbor) {
             neighbor.after(element);
-@@ -7278,23 +7492,31 @@
+@@ -7346,23 +7562,31 @@
     ) {
       if (this.isTabGroupLabel(targetElement)) {
         targetElement = targetElement.group;
@@ -968,7 +970,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       } else if (!element.pinned && targetElement && targetElement.pinned) {
         // If the caller asks to move an unpinned element next to a pinned
         // tab, move the unpinned element to be the first unpinned element
-@@ -7307,12 +7529,35 @@
+@@ -7375,12 +7599,35 @@
         //    move the tab group right before the first unpinned tab.
         // 4. Moving a tab group and the first unpinned tab is grouped:
         //    move the tab group right before the first unpinned tab's tab group.
@@ -1005,7 +1007,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       // We want to include the splitview wrapper if it's the targetElement, but
       // not in the case where we want to reverse tabs within the same splitview.
-@@ -7321,6 +7566,7 @@
+@@ -7389,6 +7636,7 @@
       }
 
       let getContainer = () =>
@@ -1013,7 +1015,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         element.pinned
           ? this.tabContainer.pinnedTabsContainer
           : this.tabContainer;
-@@ -7329,11 +7575,15 @@
+@@ -7397,11 +7645,15 @@
         element,
         () => {
           if (moveBefore) {
@@ -1030,7 +1032,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
           }
         },
         { metricsContext }
-@@ -7411,11 +7661,15 @@
+@@ -7479,11 +7731,15 @@
      *   The context for the operation for telemetry purposes.
      */
     moveTabToExistingGroup(aTab, aGroup, { metricsContext } = {}) {
@@ -1049,7 +1051,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       }
       if (aTab.group && aTab.group.id === aGroup.id) {
         return;
-@@ -7489,6 +7743,7 @@
+@@ -7557,6 +7813,7 @@
 
       let state = {
         tabIndex: tab._tPos,
@@ -1057,7 +1059,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       };
       if (tab.visible) {
         state.elementIndex = tab.elementIndex;
-@@ -7527,7 +7782,7 @@
+@@ -7595,7 +7852,7 @@
       let changedSplitView =
         previousTabState.splitViewId != currentTabState.splitViewId;
 
@@ -1066,7 +1068,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
         tab.dispatchEvent(
           new CustomEvent("TabMove", {
             bubbles: true,
-@@ -7579,6 +7834,10 @@
+@@ -7647,6 +7904,10 @@
 
       moveActionCallback();
 
@@ -1077,7 +1079,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       // Clear tabs cache after moving nodes because the order of tabs may have
       // changed.
       this.tabContainer._invalidateCachedTabs();
-@@ -7626,7 +7885,22 @@
+@@ -7694,7 +7955,22 @@
      * @returns {object}
      *    The new tab in the current window, null if the tab couldn't be adopted.
      */
@@ -1101,7 +1103,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       // Swap the dropped tab with a new one we create and then close
       // it in the other window (making it seem to have moved between
       // windows). We also ensure that the tab we create to swap into has
-@@ -7669,6 +7943,8 @@
+@@ -7737,6 +8013,8 @@
       }
       params.skipLoad = true;
       let newTab = this.addWebTab("about:blank", params);
@@ -1110,7 +1112,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
       aTab.container.tabDragAndDrop.finishAnimateTabMove();
 
-@@ -8448,7 +8724,7 @@
+@@ -8516,7 +8794,7 @@
         // preventDefault(). It will still raise the window if appropriate.
         return;
       }
@@ -1119,7 +1121,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       window.focus();
       aEvent.preventDefault();
     }
-@@ -8465,7 +8741,6 @@
+@@ -8533,7 +8811,6 @@
 
     on_TabGroupCollapse(aEvent) {
       aEvent.target.tabs.forEach(tab => {
@@ -1127,7 +1129,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
       });
     }
 
-@@ -8819,7 +9094,9 @@
+@@ -8887,7 +9164,9 @@
 
         let filter = this.#tabFilters.get(tab);
         if (filter) {
@@ -1137,7 +1139,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
 
           let listener = this.#tabListeners.get(tab);
           if (listener) {
-@@ -9604,6 +9881,7 @@
+@@ -9676,6 +9955,7 @@
             aWebProgress.isTopLevel
           ) {
             this._tab.setAttribute("busy", "true");
@@ -1145,7 +1147,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
             gBrowser._tabAttrModified(this._tab, ["busy"]);
             this._tab._notselectedsinceload = !this._tab.selected;
           }
-@@ -9684,6 +9962,7 @@
+@@ -9756,6 +10036,7 @@
         // known defaults. Note we use the original URL since about:newtab
         // redirects to a prerendered page.
         const shouldRemoveFavicon =
@@ -1153,7 +1155,7 @@ index 39b5babee5942427a82a7a64ad69e1b16efebcc1..32beac13dd4215a16de3a783db6c32da
           !this._browser.mIconURL &&
           !ignoreBlank &&
           !(originalLocation.spec in FAVICON_DEFAULTS);
-@@ -9858,13 +10137,6 @@
+@@ -9930,13 +10211,6 @@
             this._browser.originalURI = aRequest.originalURI;
           }
 
--- a/src/browser/components/urlbar/UrlbarPrefs-sys-mjs.patch
+++ b/src/browser/components/urlbar/UrlbarPrefs-sys-mjs.patch
@@ -1,8 +1,18 @@
 diff --git a/browser/components/urlbar/UrlbarPrefs.sys.mjs b/browser/components/urlbar/UrlbarPrefs.sys.mjs
-index 2d21248256c6c2bfb8dac958133c10e3251ef564..f788bd10ec2c08e4b27b77cd3bb0489fb04e8b7a 100644
+index e48f0295d803ba9eac5ab9d01ebb3b3dacbc9d4b..cb78b74230f63a47479404767b5ab5883278dfba 100644
 --- a/browser/components/urlbar/UrlbarPrefs.sys.mjs
 +++ b/browser/components/urlbar/UrlbarPrefs.sys.mjs
-@@ -462,6 +462,7 @@ const PREF_URLBAR_DEFAULTS = /** @type {PreferenceDefinition[]} */ ([
+@@ -161,6 +161,9 @@ const PREF_URLBAR_DEFAULTS = /** @type {PreferenceDefinition[]} */ ([
+   // Feature gate pref for flight status suggestions in the urlbar.
+   ["flightStatus.featureGate", false],
+ 
+  // Whether to close the urlbar when blurring the window while the urlbar is focused.
+  ["closeOnWindowBlur", true],
+
+   // The minimum prefix length of a flight status keyword the user must type to
+   // trigger the suggestion. 0 means the min length should be taken from Nimbus
+   // or remote settings.
+@@ -486,6 +489,7 @@ const PREF_URLBAR_DEFAULTS = /** @type {PreferenceDefinition[]} */ ([
   ["shortcuts.tabs", true],
   ["shortcuts.history", true],
   ["shortcuts.actions", true],
@@ -10,12 +20,12 @@ index 2d21248256c6c2bfb8dac958133c10e3251ef564..f788bd10ec2c08e4b27b77cd3bb0489f
 
   // Boolean to determine if the providers defined in `exposureResults`
   // should be displayed in search results. This can be set by a
-@@ -799,6 +800,8 @@ function makeDefaultResultGroups({ showSearchSuggestionsFirst }) {
+@@ -854,6 +858,8 @@ function makeDefaultResultGroups({
    */
   let rootGroup = {
     children: [
-+      { children: [{ group: lazy.UrlbarUtils.RESULT_GROUP.ZEN_ACTION }] },
-+      { children: [{ group: lazy.UrlbarUtils.RESULT_GROUP.ZEN_WORKSPACE }] },
+      { children: [{ group: lazy.UrlbarShared.RESULT_GROUP.ZEN_ACTION }] },
+      { children: [{ group: lazy.UrlbarShared.RESULT_GROUP.ZEN_WORKSPACE }] },
       // heuristic
       {
         maxResultCount: 1,
--- a/src/browser/components/urlbar/UrlbarProviderHeuristicFallback-sys-mjs.patch
+++ b/src/browser/components/urlbar/UrlbarProviderHeuristicFallback-sys-mjs.patch
@@ -1,8 +1,8 @@
 diff --git a/browser/components/urlbar/UrlbarProviderHeuristicFallback.sys.mjs b/browser/components/urlbar/UrlbarProviderHeuristicFallback.sys.mjs
-index f611d8e44af518aa1adc7505c5021235f55b49de..0eca20cb869626dfa6ace02acc00cad84462d54f 100644
+index cfc232f038cd491db32e0c0ca35622360dd9dec5..4806a725ddefa9d0709020d537eae5464249a294 100644
 --- a/browser/components/urlbar/UrlbarProviderHeuristicFallback.sys.mjs
 +++ b/browser/components/urlbar/UrlbarProviderHeuristicFallback.sys.mjs
-@@ -78,22 +78,26 @@ export class UrlbarProviderHeuristicFallback extends UrlbarProvider {
+@@ -77,22 +77,26 @@ export class UrlbarProviderHeuristicFallback extends UrlbarProvider {
         // Since we can't tell if this is a real URL and whether the user wants
         // to visit or search for it, we provide an alternative searchengine
         // match if the string looks like an alphanumeric origin or an e-mail.
@@ -17,7 +17,7 @@ index f611d8e44af518aa1adc7505c5021235f55b49de..0eca20cb869626dfa6ace02acc00cad8
 -              lazy.UrlUtils.REGEXP_COMMON_EMAIL.test(str))
 -          ) {
 +        let trimmedSearchString = queryContext.trimmedSearchString;
-+        let [searchCandidate] = UrlbarUtils.stripPrefixAndTrim(
+        let [searchCandidate] = lazy.UrlbarShared.stripPrefixAndTrim(
 +          trimmedSearchString,
 +          {
 +            trimSlash: true,
--- a/src/browser/components/urlbar/UrlbarUtils-sys-mjs.patch
+++ b/src/browser/components/urlbar/UrlbarUtils-sys-mjs.patch
@@ -1,41 +1,16 @@
 diff --git a/browser/components/urlbar/UrlbarUtils.sys.mjs b/browser/components/urlbar/UrlbarUtils.sys.mjs
-index 78c76bde00b6b581184cee1cd0e1756e5f2da6a4..94c713470b1240729ef2350d090b0449f3801af4 100644
+index 178cd5e84fda74a28b2de59b671b3399cc28fac4..b03c6e06de4ee9a95dcb4d33d7ac9f0b053be4e1 100644
 --- a/browser/components/urlbar/UrlbarUtils.sys.mjs
 +++ b/browser/components/urlbar/UrlbarUtils.sys.mjs
-@@ -126,6 +126,8 @@ export var UrlbarUtils = {
-     SEMANTIC_HISTORY: "semanticHistory",
-     SUGGESTED_INDEX: "suggestedIndex",
-     TAIL_SUGGESTION: "tailSuggestion",
-+    ZEN_ACTION: "zenAction",
-+    ZEN_WORKSPACE: "zenWorkspace",
-   }),
- 
-   // Defines provider types.
-@@ -274,6 +276,14 @@ export var UrlbarUtils = {
-         telemetryLabel: "actions",
-         uiLabel: "urlbar-searchmode-actions3",
-       },
-+      {
-+        source: UrlbarShared.RESULT_SOURCE.WORKSPACES,
-+        restrict: UrlbarShared.RESTRICT_TOKENS.WORKSPACE,
-+        icon: "chrome://browser/skin/zen-icons/selectable/layers.svg",
-+        pref: "shortcuts.workspaces",
-+        telemetryLabel: "workspaces",
-+        uiLabel: "urlbar-search-mode-workspaces",
-+      },
-     ]);
-   },
- 
-@@ -566,6 +576,12 @@ export var UrlbarUtils = {
-           return this.RESULT_GROUP.HEURISTIC_FALLBACK;
+@@ -214,6 +214,11 @@ export var UrlbarUtils = {
+           return UrlbarShared.RESULT_GROUP.HEURISTIC_FALLBACK;
         case "UrlbarProviderHistoryUrlHeuristic":
-           return this.RESULT_GROUP.HEURISTIC_HISTORY_URL;
+           return UrlbarShared.RESULT_GROUP.HEURISTIC_HISTORY_URL;
 +        case "ZenUrlbarProviderGlobalActions":
 +          if (result.source == UrlbarShared.RESULT_SOURCE.WORKSPACES) {
-+            return this.RESULT_GROUP.ZEN_WORKSPACE;
-+          } else {
-+            return this.RESULT_GROUP.ZEN_ACTION;
+            return UrlbarShared.RESULT_GROUP.ZEN_WORKSPACE;
 +          }
+          return UrlbarShared.RESULT_GROUP.ZEN_ACTION;
         case "UrlbarProviderOmnibox":
-           return this.RESULT_GROUP.HEURISTIC_OMNIBOX;
+           return UrlbarShared.RESULT_GROUP.HEURISTIC_OMNIBOX;
         case "UrlbarProviderRestrictKeywordsAutofill":
--- a/src/browser/components/urlbar/content/UrlbarChildController-mjs.patch
+++ b/src/browser/components/urlbar/content/UrlbarChildController-mjs.patch
@@ -1,8 +1,8 @@
 diff --git a/browser/components/urlbar/content/UrlbarChildController.mjs b/browser/components/urlbar/content/UrlbarChildController.mjs
-index a8e9d3093d046612650a17970330a8279f55833f..063a3e8adf009d6c0ddc60430bc0e7485e812b8a 100644
+index a17a4de079b69d2818388b33a2c1746cc6148c73..4fee63a22919972af08716db2d2de1c7549ff100 100644
 --- a/browser/components/urlbar/content/UrlbarChildController.mjs
 +++ b/browser/components/urlbar/content/UrlbarChildController.mjs
-@@ -258,7 +258,6 @@ export class UrlbarChildController {
+@@ -438,7 +438,6 @@ export class UrlbarChildController {
     const isMac = AppConstants.platform == "macosx";
     // Handle readline/emacs-style navigation bindings on Mac.
     if (
@@ -10,7 +10,7 @@ index a8e9d3093d046612650a17970330a8279f55833f..063a3e8adf009d6c0ddc60430bc0e748
       this.view.isOpen &&
       event.ctrlKey &&
       (event.key == "n" || event.key == "p")
-@@ -450,6 +449,8 @@ export class UrlbarChildController {
+@@ -630,6 +629,8 @@ export class UrlbarChildController {
             });
           }
           event.preventDefault();
@@ -19,3 +19,25 @@ index a8e9d3093d046612650a17970330a8279f55833f..063a3e8adf009d6c0ddc60430bc0e748
         }
         break;
       }
+@@ -934,6 +935,10 @@ export class UrlbarChildController {
+       }
+       reuseEmpty = true;
+     }
+    if (this.#input.hasAttribute?.("zen-newtab")) {
+      where = "tab";
+      reuseEmpty = true;
+    }
+     // The browser window exists only in chrome; a content-process input has no
+     // tab to reuse, so `gBrowser` is absent and the reuse is skipped.
+     if (
+@@ -943,6 +948,10 @@ export class UrlbarChildController {
+     ) {
+       where = "current";
+     }
+    if (this.window.gBrowser?.selectedTab.hasAttribute("zen-empty-tab")) {
+      // Always open in a new tab if the current tab is our empty tab.
+      return "tab";
+    }
+     return where;
+   }
+ 
--- a/src/browser/components/urlbar/content/UrlbarInput-mjs.patch
+++ b/src/browser/components/urlbar/content/UrlbarInput-mjs.patch
@@ -1,8 +1,8 @@
 diff --git a/browser/components/urlbar/content/UrlbarInput.mjs b/browser/components/urlbar/content/UrlbarInput.mjs
-index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a6182579cbaf4d 100644
+index 319fb6870ec18d87b9f1263bd960edaa39b0447c..554cc90fb2307450ddc68033968cefd1a95e28b8 100644
 --- a/browser/components/urlbar/content/UrlbarInput.mjs
 +++ b/browser/components/urlbar/content/UrlbarInput.mjs
-@@ -101,6 +101,13 @@ const lazy = XPCOMUtils.declareLazy({
+@@ -88,6 +88,13 @@ const lazy = XPCOMUtils.declareLazy({
   logger: () => UrlbarShared.getLogger({ prefix: "Input" }),
 });
 
@@ -16,7 +16,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
 const UNLIMITED_MAX_RESULTS = 99;
 
 let getBoundsWithoutFlushing = element =>
-@@ -769,7 +776,16 @@ ${
+@@ -771,7 +778,16 @@ ${
     // See _on_select().  HTMLInputElement.select() dispatches a "select"
     // event but does not set the primary selection.
     this._suppressPrimaryAdjustment = true;
@@ -33,7 +33,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     this._suppressPrimaryAdjustment = false;
   }
 
-@@ -843,6 +859,10 @@ ${
+@@ -846,6 +862,10 @@ ${
     hideSearchTerms = false,
     isSameDocument = false,
   } = {}) {
@@ -44,7 +44,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     if (!this.#isAddressbar) {
       throw new Error(
         "Cannot set URI for UrlbarInput that is not an address bar"
-@@ -1137,7 +1157,16 @@ ${
+@@ -1143,7 +1163,16 @@ ${
       this.searchModeSwitcher?.updateSearchIcon();
     }
 
@@ -61,7 +61,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
   }
 
   /**
-@@ -1626,7 +1655,11 @@ ${
+@@ -1726,7 +1755,11 @@ ${
     openParams.avoidBrowserFocus = keepViewOpen;
 
     if (!this.#providesSearchMode(result) && !keepViewOpen) {
@@ -74,7 +74,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     }
 
     if (isCanonized) {
-@@ -2974,6 +3007,42 @@ ${
+@@ -3016,6 +3049,42 @@ ${
     await this.#updateLayoutBreakoutDimensions();
   }
 
@@ -117,7 +117,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
   startLayoutExtend() {
     if (!this.#allowBreakout || this.hasAttribute("breakout-extend")) {
       // Do not expand if the Urlbar does not support being expanded or it is
-@@ -2988,6 +3057,13 @@ ${
+@@ -3030,6 +3099,13 @@ ${
     this.toggleAttribute("breakout-extend", true);
     this.#updateTextboxPosition();
 
@@ -131,7 +131,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     // Enable the animation only after the first extend call to ensure it
     // doesn't run when opening a new window.
     if (!this.hasAttribute("breakout-extend-animate")) {
-@@ -3011,6 +3087,29 @@ ${
+@@ -3053,6 +3129,29 @@ ${
       return;
     }
 
@@ -161,7 +161,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     this.toggleAttribute("breakout-extend", false);
     this.#updateTextboxPosition();
   }
-@@ -3049,7 +3148,7 @@ ${
+@@ -3091,7 +3190,7 @@ ${
     forceUnifiedSearchButtonAvailable = false
   ) {
     let prevState = this.getAttribute("pageproxystate");
@@ -170,7 +170,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     this.setAttribute("pageproxystate", state);
     this._inputContainer.setAttribute("pageproxystate", state);
     this._identityBox?.setAttribute("pageproxystate", state);
-@@ -3332,10 +3431,12 @@ ${
+@@ -3355,10 +3454,12 @@ ${
     }
 
     this.style.top = px(
@@ -183,7 +183,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     );
   }
 
-@@ -3394,9 +3495,10 @@ ${
+@@ -3417,9 +3518,10 @@ ${
           return;
         }
 
@@ -193,9 +193,9 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
 -          px(getBoundsWithoutFlushing(this.parentNode).height)
 +          px(getBoundsWithoutFlushing(this.parentNode).height + 8)
         );
-         this.style.setProperty(
-           "--urlbar-height",
-@@ -3902,6 +4004,7 @@ ${
+ 
+         if (this.#breakoutBlockerCount) {
+@@ -3929,6 +4031,7 @@ ${
   }
 
   _toggleActionOverride(event) {
@@ -203,47 +203,33 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     if (
       event.keyCode == KeyEvent.DOM_VK_SHIFT ||
       event.keyCode == KeyEvent.DOM_VK_ALT ||
-@@ -4014,8 +4117,8 @@ ${
+@@ -4027,9 +4130,10 @@ ${
     if (!this.#isAddressbar) {
       return val;
     }
-    let trimmedValue = lazy.UrlbarPrefs.get("trimURLs")
+-    let trimmedValue = UrlbarPrefs.get("trimURLs")
 -      ? lazy.BrowserUIUtils.trimURL(val)
-+    let trimmedValue = lazy.UrlbarPrefs.get("trimURLs") && this._zenTrimURL
-+      ? this._zenTrimURL(val)
-       : val;
+-      : val;
+    let trimmedValue =
+      UrlbarPrefs.get("trimURLs") && this._zenTrimURL
+        ? this._zenTrimURL(val)
+        : val;
     // Only trim value if the directionality doesn't change to RTL and we're not
     // showing a strikeout https protocol.
-@@ -4317,6 +4420,7 @@ ${
-     browser = this.window.gBrowser.selectedBrowser,
-     keepViewOpen = false
-   ) {
-+    openUILinkWhere = this.window.gZenUIManager.getOpenUILinkWhere(url, browser, openUILinkWhere);
-     if (this.#isAddressbar) {
-       this.#prepareAddressbarLoad(
-         url,
-@@ -4430,6 +4534,10 @@ ${
-       }
-       reuseEmpty = true;
-     }
-+    if (this.hasAttribute("zen-newtab")) {
-+      where = "tab";
-+      reuseEmpty = true;
-+    }
-     if (
-       where == "tab" &&
-       reuseEmpty &&
-@@ -4437,6 +4545,9 @@ ${
-     ) {
-       where = "current";
-     }
-+    if (this.window.gBrowser.selectedTab.hasAttribute("zen-empty-tab")) {
-+      return "tab"; // Always open in a new tab if the current tab is "our empty tab".
-+    }
-     return where;
-   }
- 
-@@ -4691,6 +4802,7 @@ ${
+     return this.controller.isTextDirectionRTL(trimmedValue) ||
+@@ -4235,6 +4339,11 @@ ${
+     keepViewOpen = false,
+     browserId = null,
+   }) {
+    where = this.window.gZenUIManager.getOpenUILinkWhere(
+      url,
+      this.window.gBrowser.selectedBrowser,
+      where
+    );
+     let userTypedValue;
+     if (this.#isAddressbar && where == "current") {
+       // Make sure URL is formatted properly (don't show punycode).
+@@ -4576,6 +4685,7 @@ ${
       this.setResultForCurrentValue(null);
       this.handleCommand();
       this.controller.clearLastQueryContextCache();
@@ -251,7 +237,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
 
       this._suppressStartQuery = false;
     });
-@@ -4698,7 +4810,6 @@ ${
+@@ -4583,7 +4693,6 @@ ${
     contextMenu.addEventListener("popupshowing", () => {
       // Close the results pane when the input field contextual menu is open,
       // because paste and go doesn't want a result selection.
@@ -259,7 +245,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
 
       let controller =
         this.document.commandDispatcher.getControllerForCommand("cmd_paste");
-@@ -4979,7 +5090,11 @@ ${
+@@ -4850,7 +4959,11 @@ ${
     if (!engineName && !source && !this.hasAttribute("searchmode")) {
       return;
     }
@@ -272,7 +258,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     if (this._searchModeIndicatorTitle) {
       this._searchModeIndicatorTitle.textContent = "";
       this._searchModeIndicatorTitle.removeAttribute("data-l10n-id");
-@@ -5297,6 +5412,7 @@ ${
+@@ -5149,6 +5262,7 @@ ${
 
     this.document.l10n.setAttributes(
       this.inputField,
@@ -280,7 +266,20 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
       l10nId,
       l10nId == "urlbar-placeholder-with-name"
         ? { name: engineName }
-@@ -5424,6 +5540,11 @@ ${
+@@ -5199,6 +5313,12 @@ ${
+     }
+ 
+     lazy.logger.debug("Blur Event");
+    if (
+      this.document.commandDispatcher.focusedElement == this.inputField &&
+      !UrlbarPrefs.get("closeOnWindowBlur")
+    ) {
+      return;
+    }
+     // We cannot count every blur events after a missed engagement as abandoment
+     // because the user may have clicked on some view element that executes
+     // a command causing a focus change. For example opening preferences from
+@@ -5276,6 +5396,11 @@ ${
   }
 
   _on_click(event) {
@@ -292,7 +291,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
     switch (event.target) {
       case this.inputField:
       case this._inputContainer:
-@@ -5513,10 +5634,11 @@ ${
+@@ -5371,10 +5496,11 @@ ${
       }
       if (untrim) {
         this.setValue(this._untrimmedValue);
@@ -305,7 +304,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
       this.view.autoOpen({ event });
     } else {
       if (this._untrimOnFocusAfterKeydown) {
-@@ -5556,9 +5678,16 @@ ${
+@@ -5414,9 +5540,16 @@ ${
   }
 
   _on_mousedown(event) {
@@ -323,7 +322,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
         if (
           event.composedTarget != this.inputField &&
           event.composedTarget != this._inputContainer
-@@ -5568,6 +5697,10 @@ ${
+@@ -5426,6 +5559,10 @@ ${
 
         this.focusedViaMousedown = !this.focused;
         this.#preventClickSelectsAll = this.focused;
@@ -334,7 +333,7 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
 
         // Keep the focus status, since the attribute may be changed
         // upon calling this.focus().
-@@ -5605,7 +5738,7 @@ ${
+@@ -5463,7 +5600,7 @@ ${
         // view open on tab switch, and the TabSelect event arrived earlier.
         // Also ignore mousedown on the urlbarView context menu: opening/closing the
         // view is already handled by the result opening flow.
@@ -343,12 +342,12 @@ index e7e9495e56076cd112beafb8297dece4ae4cea58..330104d245ddd0956b95377082a61825
           break;
         }
 
-@@ -5894,7 +6027,7 @@ ${
+@@ -5754,7 +5891,7 @@ ${
     // When we are in actions search mode we can show more results so
     // increase the limit.
     let maxResults =
 -      this.searchMode?.source != UrlbarShared.RESULT_SOURCE.ACTIONS
 +      this.searchMode?.source != UrlbarShared.RESULT_SOURCE.ZEN_ACTIONS
-         ? lazy.UrlbarPrefs.get("maxRichResults")
+         ? UrlbarPrefs.get("maxRichResults")
         : UNLIMITED_MAX_RESULTS;
     let options = {
--- a/src/browser/components/urlbar/content/UrlbarShared-mjs.patch
+++ b/src/browser/components/urlbar/content/UrlbarShared-mjs.patch
@@ -1,8 +1,8 @@
 diff --git a/browser/components/urlbar/content/UrlbarShared.mjs b/browser/components/urlbar/content/UrlbarShared.mjs
-index 5b45afb747bfcdbd06782186737669aa2c4c634d..f68bd009f70415b5fb513abdfe19b4427ceefbfc 100644
+index 4e67dad66ae006842abc6eed547e4a244320d57a..393b61b4d2543c73e60afd334a353f36119ae73e 100644
 --- a/browser/components/urlbar/content/UrlbarShared.mjs
 +++ b/browser/components/urlbar/content/UrlbarShared.mjs
-@@ -47,6 +47,7 @@ export const UrlbarShared = {
+@@ -100,6 +100,7 @@ export const UrlbarShared = {
     // `looksLikeOrigin()` returned `LOOKS_LIKE_ORIGIN.OTHER` for this token.
     // It may or may not be an origin.
     POSSIBLE_ORIGIN_BUT_SEARCH_ALLOWED: 12,
@@ -10,7 +10,7 @@ index 5b45afb747bfcdbd06782186737669aa2c4c634d..f68bd009f70415b5fb513abdfe19b442
   }),
 
   /**
-@@ -67,6 +68,7 @@ export const UrlbarShared = {
+@@ -120,6 +121,7 @@ export const UrlbarShared = {
     TITLE: "#",
     URL: "$",
     ACTION: ">",
@@ -18,7 +18,7 @@ index 5b45afb747bfcdbd06782186737669aa2c4c634d..f68bd009f70415b5fb513abdfe19b442
   }),
 
   // Defines UrlbarResult types.
-@@ -112,6 +114,8 @@ export const UrlbarShared = {
+@@ -165,6 +167,8 @@ export const UrlbarShared = {
     OTHER_NETWORK: 6,
     ADDON: 7,
     ACTIONS: 8,
@@ -26,9 +26,33 @@ index 5b45afb747bfcdbd06782186737669aa2c4c634d..f68bd009f70415b5fb513abdfe19b442
 +    WORKSPACES: 10,
   }),
 
-   /**
-@@ -128,6 +132,7 @@ export const UrlbarShared = {
-     if (lazy.UrlbarPrefs.get("scotchBonnet.enableOverride")) {
+   // Results are categorized into groups to help the muxer compose them.  See
+@@ -200,6 +204,8 @@ export const UrlbarShared = {
+     SEMANTIC_HISTORY: "semanticHistory",
+     SUGGESTED_INDEX: "suggestedIndex",
+     TAIL_SUGGESTION: "tailSuggestion",
+    ZEN_ACTION: "zenAction",
+    ZEN_WORKSPACE: "zenWorkspace",
+   }),
+ 
+   // Defines provider types.
+@@ -385,6 +391,14 @@ export const UrlbarShared = {
+         telemetryLabel: "actions",
+         uiLabel: "urlbar-searchmode-actions3",
+       },
+      {
+        source: this.RESULT_SOURCE.WORKSPACES,
+        restrict: this.RESTRICT_TOKENS.WORKSPACE,
+        icon: "chrome://browser/skin/zen-icons/selectable/layers.svg",
+        pref: "shortcuts.workspaces",
+        telemetryLabel: "workspaces",
+        uiLabel: "urlbar-search-mode-workspaces",
+      },
+     ]);
+   },
+ 
+@@ -402,6 +416,7 @@ export const UrlbarShared = {
+     if (UrlbarPrefs.get("scotchBonnet.enableOverride")) {
       keys.push(this.RESTRICT_TOKENS.ACTION);
     }
 +    keys.push(this.RESTRICT_TOKENS.WORKSPACE);
--- a/src/browser/components/urlbar/content/UrlbarView-mjs.patch
+++ b/src/browser/components/urlbar/content/UrlbarView-mjs.patch
@@ -1,8 +1,8 @@
 diff --git a/browser/components/urlbar/content/UrlbarView.mjs b/browser/components/urlbar/content/UrlbarView.mjs
-index 8afb2bf4a757b3ef7902f5a6e6eed6b70ca2845e..440dea1e66540ca1998cb7464b6695ac823fedcb 100644
+index 9a2c787cfa4d70bd587d49e017075f905c90f626..1c3b341e5d520ec9541c4021aaedce98751b6993 100644
 --- a/browser/components/urlbar/content/UrlbarView.mjs
 +++ b/browser/components/urlbar/content/UrlbarView.mjs
-@@ -674,7 +674,7 @@ export class UrlbarView {
+@@ -822,7 +822,7 @@ export class UrlbarView {
       !this.input.value ||
       this.input.getAttribute("pageproxystate") == "valid"
     ) {
@@ -11,7 +11,7 @@ index 8afb2bf4a757b3ef7902f5a6e6eed6b70ca2845e..440dea1e66540ca1998cb7464b6695ac
         // Try to reuse the cached top-sites context. If it's not cached, then
         // there will be a gap of time between when the input is focused and
         // when the view opens that can be perceived as flicker.
-@@ -812,10 +812,6 @@ export class UrlbarView {
+@@ -963,10 +963,6 @@ export class UrlbarView {
     }
 
     // If search mode isn't active, close the view.
@@ -22,7 +22,7 @@ index 8afb2bf4a757b3ef7902f5a6e6eed6b70ca2845e..440dea1e66540ca1998cb7464b6695ac
 
     // Search mode is active.  If the one-offs should be shown, make sure they
     // are enabled and show the view.
-@@ -3031,6 +3027,8 @@ export class UrlbarView {
+@@ -3306,6 +3302,8 @@ export class UrlbarView {
       if (row?.hasAttribute("row-selectable")) {
         row?.toggleAttribute("selected", true);
       }
@@ -31,7 +31,7 @@ index 8afb2bf4a757b3ef7902f5a6e6eed6b70ca2845e..440dea1e66540ca1998cb7464b6695ac
       if (element != row) {
         row?.toggleAttribute("descendant-selected", true);
       }
-@@ -3544,7 +3542,7 @@ export class UrlbarView {
+@@ -3972,7 +3970,7 @@ export class UrlbarView {
   }
 
   #enableOrDisableRowWrap() {
@@ -40,3 +40,16 @@ index 8afb2bf4a757b3ef7902f5a6e6eed6b70ca2845e..440dea1e66540ca1998cb7464b6695ac
     this.#rows.toggleAttribute("wrap", wrap);
     this.oneOffSearchButtons?.container.toggleAttribute("wrap", wrap);
   }
+@@ -4387,6 +4385,12 @@ export class UrlbarView {
+   }
+ 
+   on_blur() {
+    if (
+      this.document.commandDispatcher.focusedElement == this.input.inputField &&
+      !UrlbarPrefs.get("closeOnWindowBlur")
+    ) {
+      return;
+    }
+     // If the view is open without the input being focused, it will not close
+     // automatically when the window loses focus. We might be in this state
+     // after a Search Tip is shown on an engine homepage.
--- a/src/browser/themes/linux/browser-css.patch
+++ b/src/browser/themes/linux/browser-css.patch
@@ -1,11 +1,11 @@
 diff --git a/browser/themes/linux/browser.css b/browser/themes/linux/browser.css
-index e735ec80b56e1a2da4bc5bec29136ce60353277b..330ea62d220d9acd96a95a605888839388e97452 100644
+index f276db1d456703493ee713370691352985021708..619ee6724eec1e6a25adcb257af0d02eb7a29d34 100644
 --- a/browser/themes/linux/browser.css
 +++ b/browser/themes/linux/browser.css
@@ -14,7 +14,6 @@
     @media (-moz-gtk-theme-family) {
       --tabs-navbar-separator-style: none;
-       @media (prefers-color-scheme: light) and (not -moz-pref("browser.nova.enabled")) {
+       @media (prefers-color-scheme: light) {
 -        --urlbar-box-background-color: #fafafa;
       }
     }
--- a/src/browser/themes/shared/tabbrowser/content-area-css.patch
+++ b/src/browser/themes/shared/tabbrowser/content-area-css.patch
@@ -1,16 +1,16 @@
 diff --git a/browser/themes/shared/tabbrowser/content-area.css b/browser/themes/shared/tabbrowser/content-area.css
-index 3acdec2b8e043fe27919cfa54e73f4d3c491bfc8..267a1087134464a8193a824a2d7f8ac15ff8ad60 100644
+index 2374ed38bd9361d6c7e1886117099c6761e403b8..72f1f52a13096f19ca4009037ad0cdc880775ff7 100644
 --- a/browser/themes/shared/tabbrowser/content-area.css
 +++ b/browser/themes/shared/tabbrowser/content-area.css
-@@ -157,7 +157,6 @@
-   min-height: 0;
+@@ -239,7 +239,6 @@
+   min-width: 0;
 
   /* We want to be able to show the frame color behind the clipped radiused corner */
 -  background: var(--tabpanel-background-color);
 
-   @media -moz-pref("sidebar.revamp") {
-     outline: 0.01px solid var(--chrome-content-separator-color);
-@@ -216,7 +215,6 @@
+   display: grid;
+   /**
+@@ -425,7 +424,6 @@
   }
 
   browser:is([blank], [pendingpaint]) {
@@ -18,7 +18,7 @@ index 3acdec2b8e043fe27919cfa54e73f4d3c491bfc8..267a1087134464a8193a824a2d7f8ac1
   }
 
   /* Exclude browsers with smartwindow-content attribute which inherit
-@@ -553,7 +551,7 @@ split-view-footer {
+@@ -865,7 +863,7 @@ split-view-footer {
 
 .dialogStack {
   z-index: var(--browser-stack-z-index-dialog-stack);
@@ -27,12 +27,12 @@ index 3acdec2b8e043fe27919cfa54e73f4d3c491bfc8..267a1087134464a8193a824a2d7f8ac1
   inset: 0;
   /* --browser-with-dialog set on browser[tabDialogShowing], we want to position the overlay
      only on the top of the <browser> element so it doesn't overlap the DevTools toolbox */
-@@ -718,7 +716,7 @@ split-view-footer {
+@@ -1034,7 +1032,7 @@ split-view-footer {
 
 .dialogOverlay[topmost="true"],
 #window-modal-dialog::backdrop {
 -  background-color: var(--background-color-overlay);
 +  background-color: light-dark(rgba(255, 255, 255, .3), rgba(0, 0, 0, .3));
- }
+   border-radius: var(--chrome-block-radius);
 
- .dialogOverlay[hideContent="true"][topmost="true"] {
+   .browserSidebarContainer.responsive-mode & {
--- a/src/browser/themes/shared/tabbrowser/tabs-css.patch
+++ b/src/browser/themes/shared/tabbrowser/tabs-css.patch
@@ -1,17 +1,17 @@
 diff --git a/browser/themes/shared/tabbrowser/tabs.css b/browser/themes/shared/tabbrowser/tabs.css
-index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f253804576e 100644
+index 61c0b8382c78f63ad9113af55a6236c4a29bc45b..0ab463c768d4fb3f45d22e753f408c46b61c0480 100644
 --- a/browser/themes/shared/tabbrowser/tabs.css
 +++ b/browser/themes/shared/tabbrowser/tabs.css
-@@ -45,7 +45,7 @@
+@@ -46,7 +46,7 @@
   --tab-group-line-thickness: 2px;
   --tab-group-line-toolbar-border-distance: 1px;
   /* Collapsed tabs should be square, so set width to match the min height */
 -  --tab-collapsed-background-width: var(--tab-min-height);
 +  --tab-collapsed-background-width: 48px;
   --tab-collapsed-width: calc(var(--tab-collapsed-background-width) + 2 * var(--tab-inner-inline-margin));
+   --tab-collapsed-split-pill-offset: 0px;
   --tab-pinned-min-width-expanded: calc(var(--tab-pinned-expanded-background-width) + 2 * var(--tab-pinned-margin-inline-expanded));
-   --tab-note-icon-end-margin: var(--dimension-4);
-@@ -295,7 +295,6 @@ tab-split-view-wrapper[dragtarget] {
+@@ -308,7 +308,6 @@ tab-split-view-wrapper[dragtarget] {
   }
 
   :root:not([uidensity="compact"], [sidebar-expand-on-hover]) &[pinned] {
@@ -19,7 +19,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
   }
 
   &:is([selected], [multiselected]) {
-@@ -309,6 +308,7 @@ tab-split-view-wrapper[dragtarget] {
+@@ -322,6 +321,7 @@ tab-split-view-wrapper[dragtarget] {
     border-radius: inherit;
     position: relative;
     overflow: hidden;
@@ -27,7 +27,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
 
     &::before {
       position: absolute;
-@@ -506,10 +506,6 @@ tab-split-view-wrapper[dragtarget] {
+@@ -519,10 +519,6 @@ tab-split-view-wrapper[dragtarget] {
 
   @media -moz-pref("browser.tabs.fadeOutUnloadedTabs") {
     &[pending] {
@@ -38,7 +38,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
       opacity: 0.5;
       /* Fade the favicon out */
       transition-property: filter, opacity;
-@@ -525,10 +521,6 @@ tab-split-view-wrapper[dragtarget] {
+@@ -538,10 +534,6 @@ tab-split-view-wrapper[dragtarget] {
 
   @media -moz-pref("browser.tabs.fadeOutExplicitlyUnloadedTabs") {
     &[pending][discarded] {
@@ -49,7 +49,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
       opacity: 0.5;
       /* Fade the favicon out */
       transition-property: filter, opacity;
-@@ -602,7 +594,7 @@ tab-split-view-wrapper[dragtarget] {
+@@ -615,7 +607,7 @@ tab-split-view-wrapper[dragtarget] {
   }
 
   #tabbrowser-tabs[orient="vertical"] & {
@@ -58,7 +58,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
   }
 
   &[crashed] {
-@@ -610,7 +602,7 @@ tab-split-view-wrapper[dragtarget] {
+@@ -623,7 +615,7 @@ tab-split-view-wrapper[dragtarget] {
   }
 
   #tabbrowser-tabs[orient="vertical"]:not([expanded]) &:not([crashed]),
@@ -67,7 +67,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
     &[soundplaying] {
       list-style-image: url("chrome://browser/skin/tabbrowser/tab-audio-playing-small.svg");
     }
-@@ -664,7 +656,7 @@ tab-split-view-wrapper[dragtarget] {
+@@ -677,7 +669,7 @@ tab-split-view-wrapper[dragtarget] {
     }
   }
 
@@ -76,7 +76,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
   &[crashed] {
     display: revert;
   }
-@@ -824,7 +816,7 @@ tab-split-view-wrapper[dragtarget] {
+@@ -837,7 +829,7 @@ tab-split-view-wrapper[dragtarget] {
       has not been added to root. There are certain scenarios when that attribute is temporarily
       removed from root such as when toggling the sidebar to expand with the toolbar button. */
     #tabbrowser-tabs[orient="horizontal"] &:not([pinned]):not([crashed]),
@@ -85,7 +85,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
       &:is([soundplaying], [muted], [activemedia-blocked]) {
         display: flex;
       }
-@@ -1044,7 +1036,6 @@ tab-split-view-wrapper[dragtarget] {
+@@ -1151,7 +1143,6 @@ tab-split-view-wrapper[dragtarget] {
 .tabbrowser-tab:is([image], [pinned]) > .tab-stack > .tab-content[attention]:not([selected]),
 .tabbrowser-tab > .tab-stack > .tab-content[pinned][titlechanged]:not([selected]),
 #tabbrowser-tabs[orient="vertical"] .tabbrowser-tab > .tab-stack > .tab-content[titlechanged]:not([selected]) {
@@ -93,7 +93,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
   background-position: center bottom 6.5px;
   background-size: 4px 4px;
   background-repeat: no-repeat;
-@@ -1797,7 +1788,7 @@ tab-group {
+@@ -1904,7 +1895,7 @@ tab-group {
 }
 
 #tabbrowser-tabs[orient="vertical"][expanded] {
@@ -102,7 +102,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
   &[movingtab][movingtab-addToGroup]:not([movingtab-group], [movingtab-ungroup]) .tabbrowser-tab:is(:active, [multiselected]) {
     margin-inline-start: var(--space-medium);
   }
-@@ -2351,7 +2342,7 @@ tab-group {
+@@ -2504,7 +2495,7 @@ tab-group {
   }
 }
 
@@ -111,8 +111,8 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
 #vertical-tabs-newtab-button {
   appearance: none;
   min-height: var(--tab-min-height);
-@@ -2362,7 +2353,7 @@ tab-group {
-   margin-inline: var(--tab-inner-inline-margin);
+@@ -2524,7 +2515,7 @@ tab-group {
+   }
 
   #tabbrowser-tabs[orient="vertical"]:not([expanded]) & > .toolbarbutton-text {
 -    display: none;
@@ -120,7 +120,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
   }
 
   &:hover {
-@@ -2386,7 +2377,7 @@ tab-group {
+@@ -2548,7 +2539,7 @@ tab-group {
  * flex container. #tabs-newtab-button is a child of the arrowscrollbox where
  * we don't want a gap (between tabs), so we have to add some margin.
  */
@@ -129,7 +129,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
   margin-block: var(--tab-margin-block);
 }
 
-@@ -2576,7 +2567,6 @@ tab-group {
+@@ -2740,7 +2731,6 @@ tab-group {
 
   &:not([expanded]) {
     .tabbrowser-tab[pinned] {
@@ -137,7 +137,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
     }
 
     .tab-background {
-@@ -2615,8 +2605,8 @@ tab-group {
+@@ -2779,8 +2769,8 @@ tab-group {
       display: block;
       position: absolute;
       inset: auto;
@@ -148,7 +148,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
 
       &:-moz-window-inactive {
         background-image:
-@@ -2714,9 +2704,6 @@ tab-group {
+@@ -2878,9 +2868,6 @@ tab-group {
   ~ #tabbrowser-tabs[orient="horizontal"]::before {
     display: flex;
     content: "";
@@ -158,7 +158,7 @@ index 0820fa040642ee05c2a24f5d2cfa58da5c926647..2d93abcce1729744e5963f1c6ad47f25
   }
 }
 
-@@ -2749,7 +2736,6 @@ toolbar:not(#TabsToolbar) #firefox-view-button {
+@@ -2913,7 +2900,6 @@ toolbar:not(#TabsToolbar) #firefox-view-button {
   list-style-image: url(chrome://global/skin/icons/plus.svg);
 }
 
--- a/src/browser/themes/shared/urlbar-searchbar-css.patch
+++ b/src/browser/themes/shared/urlbar-searchbar-css.patch
@@ -1,19 +1,19 @@
 diff --git a/browser/themes/shared/urlbar-searchbar.css b/browser/themes/shared/urlbar-searchbar.css
-index 22d624d718a289dd7b84ffc2f04dd35893dfbe95..4f57f7853f3043e3ad01d893aa928b9d2e6f3c16 100644
+index 149f123e26cd79e89432dfeb504ca7218ee04810..7e0e6d981d6c2aa53bc2a76d82d2078419659065 100644
 --- a/browser/themes/shared/urlbar-searchbar.css
 +++ b/browser/themes/shared/urlbar-searchbar.css
@@ -19,8 +19,8 @@
 
   @media not -moz-pref("browser.nova.enabled") {
-     --urlbar-basic-component-size: calc(var(--urlbar-min-height) - 2 * (var(--urlbar-input-container-border-width) + var(--urlbar-input-container-padding)));
-    --urlbar-icon-padding: calc((var(--urlbar-min-height) - 2px /* border */ - 2px /* padding */ - 16px /* icon */) / 2);
+     --urlbar-basic-component-size: calc(var(--urlbar-height) - 2 * (var(--urlbar-input-container-border-width) + var(--urlbar-input-container-padding)));
+-    --urlbar-icon-padding: calc((var(--urlbar-height) - 2px /* border */ - 2px /* padding */ - 16px /* icon */) / 2);
 -    --urlbar-input-container-padding: round(up, 1px, env(hairline));
-+    --urlbar-icon-padding: calc((var(--urlbar-min-height) - 2px /* border */ - 14px /* icon */) / 2);
+    --urlbar-icon-padding: calc((var(--urlbar-height) - 2px /* border */ - 14px /* icon */) / 2);
 +    --urlbar-input-container-padding: 2px;
   }
   @media (max-width: 770px) {
     --urlbar-container-min-width: 240px;
-@@ -126,7 +126,7 @@ toolbar[inactive="true"] .urlbar,
+@@ -127,7 +127,7 @@ toolbar[inactive="true"] .urlbar,
 .urlbar:not([usertyping]) > .urlbar-input-container > .urlbar-go-button,
 .urlbar:not(#searchbar-new, [focused]) > .urlbar-input-container > .urlbar-go-button,
 #urlbar-revert-button-container {
@@ -22,7 +22,7 @@ index 22d624d718a289dd7b84ffc2f04dd35893dfbe95..4f57f7853f3043e3ad01d893aa928b9d
 }
 
 /* Document Picture-in-Picture API window */
-@@ -403,6 +403,10 @@ toolbar[inactive="true"] .urlbar,
+@@ -405,6 +405,10 @@ toolbar[inactive="true"] .urlbar,
   .urlbar:not([focused])[textoverflow="left"][domaindir="rtl"] > .urlbar-input-container > .urlbar-input-box > & {
     mask-image: linear-gradient(to right, transparent var(--urlbar-scheme-size), black calc(var(--urlbar-scheme-size) + 3ch));
   }
@@ -33,16 +33,18 @@ index 22d624d718a289dd7b84ffc2f04dd35893dfbe95..4f57f7853f3043e3ad01d893aa928b9d
 }
 
 #urlbar-scheme {
-@@ -492,10 +496,14 @@ toolbar[inactive="true"] .urlbar,
+@@ -476,10 +480,15 @@ toolbar[inactive="true"] .urlbar,
+   }
 
   .urlbar[breakout][breakout-extend] {
-     height: auto;
+-    margin-left: calc(-1 * var(--urlbar-margin-inline));
 +    align-items: center;
-+    :root:not([zen-single-toolbar='true']) & {
-     margin-left: calc(-1 * var(--urlbar-margin-inline));
-+    }
     width: calc(var(--urlbar-width) + 2 * var(--urlbar-margin-inline));
 
+    :root:not([zen-single-toolbar="true"]) & {
+      margin-left: calc(-1 * var(--urlbar-margin-inline));
+    }
+
     > .urlbar-input-container {
 +      align-items: center;
       height: var(--urlbar-container-height);
--- a/src/external-patches/firefox/add_urlbar_closeonwindowblur_preference.patch
+++ b/src/external-patches/firefox/add_urlbar_closeonwindowblur_preference.patch
@@ -1,76 +0,0 @@
-diff --git a/browser/app/profile/firefox.js b/browser/app/profile/firefox.js
--- a/browser/app/profile/firefox.js
-+++ b/browser/app/profile/firefox.js
-@@ -411,10 +411,13 @@
- pref("browser.urlbar.maxRichResults", 10);
- 
- // The maximum number of historical search results to show.
- pref("browser.urlbar.maxHistoricalSearchSuggestions", 2);
- 
-+// Whether to close the urlbar when blurring the window while the urlbar is focused.
-+pref("browser.urlbar.closeOnWindowBlur", true);
-+
- // The default behavior for the urlbar can be configured to use any combination
- // of the match filters with each additional filter adding more results (union).
- pref("browser.urlbar.suggest.bookmark",             true);
- pref("browser.urlbar.suggest.clipboard",            true);
- pref("browser.urlbar.suggest.history",              true);
-diff --git a/browser/components/urlbar/UrlbarPrefs.sys.mjs b/browser/components/urlbar/UrlbarPrefs.sys.mjs
--- a/browser/components/urlbar/UrlbarPrefs.sys.mjs
-+++ b/browser/components/urlbar/UrlbarPrefs.sys.mjs
-@@ -152,10 +152,13 @@
-   ["filter.javascript", true],
- 
-   // Feature gate pref for flight status suggestions in the urlbar.
-   ["flightStatus.featureGate", false],
- 
-+  // Whether to close the urlbar when blurring the window while the urlbar is focused.
-+  ["closeOnWindowBlur", true],
-+
-   // The minimum prefix length of a flight status keyword the user must type to
-   // trigger the suggestion. 0 means the min length should be taken from Nimbus
-   // or remote settings.
-   ["flightStatus.minKeywordLength", 0],
- 
-diff --git a/browser/components/urlbar/content/UrlbarView.mjs b/browser/components/urlbar/content/UrlbarView.mjs
--- a/browser/components/urlbar/content/UrlbarView.mjs
-+++ b/browser/components/urlbar/content/UrlbarView.mjs
-@@ -3909,10 +3909,16 @@
-       }
-     }
-   }
- 
-   on_blur() {
-+    if (
-+      this.document.commandDispatcher.focusedElement == this.input.inputField &&
-+      !lazy.UrlbarPrefs.get("closeOnWindowBlur")
-+    ) {
-+      return;
-+    }
-     // If the view is open without the input being focused, it will not close
-     // automatically when the window loses focus. We might be in this state
-     // after a Search Tip is shown on an engine homepage.
-     if (!lazy.UrlbarPrefs.get("ui.popup.disable_autohide")) {
-       this.close();
-diff --git a/browser/components/urlbar/content/UrlbarInput.mjs b/browser/components/urlbar/content/UrlbarInput.mjs
--- a/browser/components/urlbar/content/UrlbarInput.mjs
-+++ b/browser/components/urlbar/content/UrlbarInput.mjs
-@@ -5460,11 +5460,17 @@
-   _on_blur(event) {
-     if (this.view.resultMenu.hasAttribute("open")) {
-       return;
-     }
- 
-     lazy.logger.debug("Blur Event");
-+    if (
-+      this.document.commandDispatcher.focusedElement == this.inputField &&
-+      !lazy.UrlbarPrefs.get("closeOnWindowBlur")
-+    ) {
-+      return;
-+    }
-     // We cannot count every blur events after a missed engagement as abandoment
-     // because the user may have clicked on some view element that executes
-     // a command causing a focus change. For example opening preferences from
-     // the oneoff settings button.
-     // For now we detect that case by discarding the event on command, but we
-     // may want to figure out a more robust way to detect abandonment.
--- a/src/external-patches/firefox/allow_backdrop_to_work_on_transparency.patch
+++ b/src/external-patches/firefox/allow_backdrop_to_work_on_transparency.patch
@@ -31,12 +31,13 @@ diff --git a/gfx/webrender_bindings/src/bindings.rs b/gfx/webrender_bindings/src
 
     // Ensure the WR profiler callbacks are hooked up to the Gecko profiler.
     set_profiler_hooks(Some(&PROFILER_HOOKS));
-@@ -2164,10 +2165,11 @@
+@@ -2164,11 +2165,12 @@
         texture_cache_config,
         reject_software_rasterizer,
         low_quality_pinch_zoom,
         max_shared_surface_size,
         enable_dithering,
+         enable_shared_instance_buffer,
 +        opaque_backdrop_fallback,
         ..Default::default()
     };
@@ -73,8 +74,9 @@ diff --git a/gfx/wr/webrender/src/renderer/init.rs b/gfx/wr/webrender/src/render
 +    /// See explanation of `gfx.webrender.opaque-backdrop-fallback`.
 +    pub opaque_backdrop_fallback: bool,
 }
-@@ -277,9 +279,10 @@
+@@ -277,10 +279,11 @@
             enable_instancing: true,
+             enable_shared_instance_buffer: false,
             reject_software_rasterizer: false,
             low_quality_pinch_zoom: false,
             max_shared_surface_size: 2048,
@@ -84,12 +86,13 @@ diff --git a/gfx/wr/webrender/src/renderer/init.rs b/gfx/wr/webrender/src/render
     }
 }
 
-@@ -802,10 +805,11 @@
+@@ -802,11 +805,12 @@
         allocated_native_surfaces: FastHashSet::default(),
         debug_overlay_state: DebugOverlayState::new(),
         buffer_damage_tracker: BufferDamageTracker::default(),
         max_primitive_instance_count,
         enable_instancing: options.enable_instancing,
+         use_shared_instance_buffer,
 +        opaque_backdrop_fallback: options.opaque_backdrop_fallback,
         consecutive_oom_frames: 0,
         target_frame_publish_id: None,
@@ -99,11 +102,14 @@ diff --git a/gfx/wr/webrender/src/renderer/init.rs b/gfx/wr/webrender/src/render
 diff --git a/gfx/wr/webrender/src/renderer/mod.rs b/gfx/wr/webrender/src/renderer/mod.rs
 --- a/gfx/wr/webrender/src/renderer/mod.rs
 +++ b/gfx/wr/webrender/src/renderer/mod.rs
-@@ -867,10 +867,12 @@
+@@ -867,13 +867,15 @@
     buffer_damage_tracker: BufferDamageTracker,
 
     max_primitive_instance_count: usize,
     enable_instancing: bool,
+     /// If true, stream instance data into large buffers shared by multiple
+     /// draws, rather than allocating a new instance buffer for each draw.
+     use_shared_instance_buffer: bool,
 
 +    opaque_backdrop_fallback: bool,
 +
--- a/src/external-patches/firefox/bug_2011236.patch
+++ b/src/external-patches/firefox/bug_2011236.patch
@@ -0,0 +1,168 @@
+diff --git a/browser/components/sessionstore/test/browser.toml b/browser/components/sessionstore/test/browser.toml
+--- a/browser/components/sessionstore/test/browser.toml
+++ b/browser/components/sessionstore/test/browser.toml
+@@ -14,10 +14,12 @@
+   "browser_frame_history_c.html",
+   "browser_frame_history_c1.html",
+   "browser_frame_history_c2.html",
+   "browser_formdata_format_sample.html",
+   "browser_sessionHistory_slow.sjs",
+  "browser_policy_container_sample.html",
+  "browser_policy_container_sample_frame.html",
+   "browser_scrollPositions_sample.html",
+   "browser_scrollPositions_sample2.html",
+   "browser_scrollPositions_sample_frameset.html",
+   "browser_scrollPositions_readerModeArticle.html",
+   "browser_sessionStorage.html",
+@@ -226,10 +228,12 @@
+ ["browser_pinned_tabs.js"]
+ skip-if = [
+   "ccov", # Bug 1625525
+ ]
+ 
+["browser_policy_container_not_stored.js"]
+
+ ["browser_privatetabs.js"]
+ 
+ ["browser_purge_domaindata.js"]
+ 
+ ["browser_purge_shistory.js"]
+diff --git a/browser/components/sessionstore/test/browser_policy_container_not_stored.js b/browser/components/sessionstore/test/browser_policy_container_not_stored.js
+new file mode 100644
+--- /dev/null
+++ b/browser/components/sessionstore/test/browser_policy_container_not_stored.js
+@@ -0,0 +1,51 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/**
+ * A session history entry only needs to retain the policy container for loads
+ * that inherit their policies (about:blank, about:srcdoc, blob:, data:, ...).
+ * Anything fetched over the network gets its policies from the response again,
+ * so storing them would only bloat the session store (bug 2011236).
+ */
+
+const TEST_ROOT = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.com"
+);
+const PARENT_URL = TEST_ROOT + "browser_policy_container_sample.html";
+const FRAME_URL = TEST_ROOT + "browser_policy_container_sample_frame.html";
+
+add_task(async function test_policy_container_only_for_inheriting_loads() {
+  const tab = BrowserTestUtils.addTab(gBrowser, PARENT_URL);
+  gBrowser.selectedTab = tab;
+  await promiseBrowserLoaded(tab.linkedBrowser, true, PARENT_URL);
+  await TabStateFlusher.flush(tab.linkedBrowser);
+
+  const state = JSON.parse(ss.getTabState(tab));
+  const topEntry = state.entries.at(-1);
+  is(topEntry.url, PARENT_URL, "collected the parent entry");
+
+  const children = topEntry.children ?? [];
+  const networkFrame = children.find(child => child.url === FRAME_URL);
+  const blankFrame = children.find(child => child.url === "about:blank");
+
+  ok(networkFrame, "collected the network-scheme subframe entry");
+  ok(blankFrame, "collected the about:blank subframe entry");
+
+  // The parent has a CSP, so both subframes inherit a policy container onto
+  // their load state. Only the one that cannot recover it from a response
+  // should keep it in session history.
+  ok(
+    !("policyContainer" in networkFrame),
+    "https subframe entry does not store a policyContainer"
+  );
+  ok(
+    "policyContainer" in blankFrame,
+    "about:blank subframe entry still stores its inherited policyContainer"
+  );
+
+  await BrowserTestUtils.removeTab(tab);
+});
+diff --git a/browser/components/sessionstore/test/browser_policy_container_sample.html b/browser/components/sessionstore/test/browser_policy_container_sample.html
+new file mode 100644
+--- /dev/null
+++ b/browser/components/sessionstore/test/browser_policy_container_sample.html
+@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <meta http-equiv="Content-Security-Policy" content="default-src * data: blob: 'unsafe-inline'">
+  <title>policyContainer session store sample</title>
+</head>
+<body>
+  <iframe id="network" src="browser_policy_container_sample_frame.html"></iframe>
+  <iframe id="blank" src="about:blank"></iframe>
+</body>
+</html>
+diff --git a/browser/components/sessionstore/test/browser_policy_container_sample_frame.html b/browser/components/sessionstore/test/browser_policy_container_sample_frame.html
+new file mode 100644
+--- /dev/null
+++ b/browser/components/sessionstore/test/browser_policy_container_sample_frame.html
+@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>policyContainer session store sample frame</title>
+</head>
+<body>
+  frame
+</body>
+</html>
+diff --git a/docshell/shistory/SessionHistoryEntry.cpp b/docshell/shistory/SessionHistoryEntry.cpp
+--- a/docshell/shistory/SessionHistoryEntry.cpp
+++ b/docshell/shistory/SessionHistoryEntry.cpp
+@@ -41,10 +41,18 @@
+ extern mozilla::LazyLogModule gSHLog;
+ 
+ namespace mozilla {
+ namespace dom {
+ 
+// Only store policy container for loads that can't carry it themselves
+// (about:blank, about:srcdoc, blob:, data:, ...)
+// bug 1867137, bug 2011236
+static nsIPolicyContainer* PolicyContainerToStore(
+    nsIURI* aURI, nsIPolicyContainer* aPolicyContainer) {
+  return CSP_ShouldURIInheritCSP(aURI) ? aPolicyContainer : nullptr;
+}
+
+ SessionHistoryInfo::SessionHistoryInfo(nsDocShellLoadState* aLoadState,
+                                        nsIChannel* aChannel)
+     : mURI(aLoadState->URI()),
+       mOriginalURI(aLoadState->OriginalURI()),
+       mResultPrincipalURI(aLoadState->ResultPrincipalURI()),
+@@ -59,11 +67,12 @@
+       mLoadReplace(aLoadState->LoadReplace()),
+       mHasUserActivation(aLoadState->HasValidUserGestureActivation()),
+       mSharedState(SharedState::Create(
+           aLoadState->TriggeringPrincipal(), aLoadState->PrincipalToInherit(),
+           aLoadState->PartitionedPrincipalToInherit(),
+-          aLoadState->PolicyContainer(),
+          PolicyContainerToStore(aLoadState->URI(),
+                                 aLoadState->PolicyContainer()),
+           /* FIXME Is this correct? */
+           aLoadState->TypeHint())) {
+   MOZ_DIAGNOSTIC_ASSERT(!mURI->SchemeIs("javascript"));
+ 
+   // Pull the upload stream off of the channel instead of the load state, as
+@@ -124,11 +133,12 @@
+   loadInfo->GetPrincipalToInherit(
+       getter_AddRefs(mSharedState.Get()->mPrincipalToInherit));
+ 
+   mSharedState.Get()->mPartitionedPrincipalToInherit =
+       aPartitionedPrincipalToInherit;
+-  mSharedState.Get()->mPolicyContainer = aPolicyContainer;
+  mSharedState.Get()->mPolicyContainer =
+      PolicyContainerToStore(mURI, aPolicyContainer);
+   aChannel->GetContentType(mSharedState.Get()->mContentType);
+   aChannel->GetOriginalURI(getter_AddRefs(mOriginalURI));
+ 
+   uint32_t loadFlags;
+   aChannel->GetLoadFlags(&loadFlags);
+
--- a/src/external-patches/firefox/css_corner_shape_rendering.patch
+++ b/src/external-patches/firefox/css_corner_shape_rendering.patch
--- a/src/external-patches/firefox/issue_14710.patch
+++ b/src/external-patches/firefox/issue_14710.patch
@@ -0,0 +1,55 @@
+diff --git a/toolkit/components/pictureinpicture/PictureInPicture.sys.mjs b/toolkit/components/pictureinpicture/PictureInPicture.sys.mjs
+--- a/toolkit/components/pictureinpicture/PictureInPicture.sys.mjs
+++ b/toolkit/components/pictureinpicture/PictureInPicture.sys.mjs
+@@ -119,10 +119,19 @@
+       }
+       case "PictureInPicture:VideoTabHidden": {
+         if (!lazy.PIP_ENABLED || !lazy.PIP_WHEN_SWITCHING_TABS) {
+           break;
+         }
+
+        // Suppress auto-toggle if the user deliberately closed this PiP window
+        if (
+          PictureInPicture.weakAutoPipBrowserClosedDeliberately.has(browser)
+        ) {
+          PictureInPicture.weakAutoPipBrowserClosedDeliberately.delete(browser);
+          break;
+        }
+
+         // If the tab is still selected, then we can ignore this event
+         if (browser.documentGlobal.gBrowser.selectedBrowser == browser) {
+           break;
+         }
+         let actor = browsingContext.currentWindowGlobal.getActor(
+@@ -261,10 +270,12 @@
+   maxConcurrentPlayerCount: 0,
+ 
+   // Maps auto pip browser to PictureInPictureParent actor
+   weakAutoPipBrowserToParent: new WeakMap(),
+ 
+  weakAutoPipBrowserClosedDeliberately: new WeakSet(),
+
+   /**
+    * Returns the player window if one exists and if it hasn't yet been closed.
+    *
+    * @param {PictureInPictureParent} pipActorRef
+    *   Reference to the calling PictureInPictureParent actor
+@@ -899,10 +910,17 @@
+     const { reason, actorRef } = closeData;
+     const win = this.getWeakPipPlayer(actorRef);
+     if (!win) {
+       return;
+     }
+
+    const browser = this.weakWinToBrowser.get(win);
+
+    if (reason === "CloseButton") {
+      PictureInPicture.weakAutoPipBrowserClosedDeliberately.add(browser);
+    }
+
+     this.removePiPBrowserFromWeakMap(this.weakWinToBrowser.get(win));
+     this.weakAutoPipBrowserToParent.delete(this.weakWinToBrowser.get(win));
+ 
+     Glean.pictureinpicture["closedMethod" + reason].record();
+     await this.closePipWindow(win);
+
--- a/src/external-patches/manifest.json
+++ b/src/external-patches/manifest.json
@@ -7,14 +7,6 @@
    "id": "D299584",
    "name": "Native MacOS popovers fix"
  },
-  {
-    "type": "phabricator",
-    "id": "D284404",
-    "name": "Add urlbar closeOnWindowBlur preference",
-    "replaces": {
-      "\n\n": "\n     // may want to figure out a more robust way to detect abandonment."
-    }
-  },
  {
    "type": "local",
    // TODO: Convert into https://phabricator.services.mozilla.com/D298079
@@ -48,5 +40,19 @@
      "this._lastJsonLength = uncompressedBytes;": "this._lastJsonLength = uncompressedBytes.jsonLength;",
      "          jsonLengthHint,": "          lengthHint: jsonLengthHint,"
    }
+  },
+  {
+    "type": "phabricator",
+    "id": "D320897",
+    "name": "Bug 2011236"
+  },
+  {
+    "type": "phabricator",
+    "id": "D321446",
+    "name": "Issue 14710"
+  },
+  {
+    "type": "local",
+    "path": "firefox/css_corner_shape_rendering.patch"
  }
 ]
--- a/src/layout/style/StyleColor-cpp.patch
+++ b/src/layout/style/StyleColor-cpp.patch
@@ -1,16 +1,16 @@
 diff --git a/layout/style/StyleColor.cpp b/layout/style/StyleColor.cpp
-index bbee32af30f35525730a10d0b242c0e8a8fe4695..a590fff105b30bc96fa7a0d8a8d3b1d5aa997e08 100644
+index f922f7fdacc7e1a14beb8da77b48aef3f6ae0b2b..47d19242baaf2a1f25ee07c6e210c839cc7b5089 100644
 --- a/layout/style/StyleColor.cpp
 +++ b/layout/style/StyleColor.cpp
-@@ -9,6 +9,7 @@
- #include "mozilla/dom/BindingDeclarations.h"
+@@ -8,6 +8,7 @@
+ #include "mozilla/StyleColorInlines.h"
 #include "nsIFrame.h"
 #include "nsStyleStruct.h"
 +#include "mozilla/nsZenBoostsBackend.h"
+ #include "nsStyleUtil.h"
 
 namespace mozilla {
- 
-@@ -96,23 +97,24 @@ StyleAbsoluteColor StyleColor::ResolveColor(
+@@ -98,23 +99,24 @@ StyleAbsoluteColor StyleColor::ResolveColor(
 
 template <>
 nscolor StyleColor::CalcColor(nscolor aColor) const {
@@ -40,7 +40,7 @@ index bbee32af30f35525730a10d0b242c0e8a8fe4695..a590fff105b30bc96fa7a0d8a8d3b1d5
 }
 
 StyleAbsoluteColor StyleAbsoluteColor::ToColorSpace(
-@@ -120,7 +122,7 @@ StyleAbsoluteColor StyleAbsoluteColor::ToColorSpace(
+@@ -122,7 +124,7 @@ StyleAbsoluteColor StyleAbsoluteColor::ToColorSpace(
   return Servo_ConvertColorSpace(this, aColorSpace);
 }
 
@@ -49,7 +49,7 @@ index bbee32af30f35525730a10d0b242c0e8a8fe4695..a590fff105b30bc96fa7a0d8a8d3b1d5
   constexpr StyleColorSpace DEST_COLOR_SPACE = StyleColorSpace::Srgb;
 
   constexpr float MIN = 0.0f;
-@@ -162,11 +164,13 @@ nscolor StyleAbsoluteColor::ToColor() const {
+@@ -164,11 +166,13 @@ nscolor StyleAbsoluteColor::ToColor() const {
     }
   }
 
--- a/src/layout/svg/SVGImageContext-h.patch
+++ b/src/layout/svg/SVGImageContext-h.patch
@@ -1,5 +1,5 @@
 diff --git a/layout/svg/SVGImageContext.h b/layout/svg/SVGImageContext.h
-index b1f811989697966e30859610f4fc07579d0385ab..f6f4cd5a45fc49b416111d980fab4e612788903e 100644
+index ad833c7c2ee6a4c4984efdb0d59e3576c2d1bc19..36864a34badc0cbfe44d6295798622fd6178f9e3 100644
 --- a/layout/svg/SVGImageContext.h
 +++ b/layout/svg/SVGImageContext.h
@@ -6,6 +6,7 @@
@@ -44,7 +44,7 @@ index b1f811989697966e30859610f4fc07579d0385ab..f6f4cd5a45fc49b416111d980fab4e61
   const Maybe<SVGPreserveAspectRatio>& GetPreserveAspectRatio() const {
     return mPreserveAspectRatio;
   }
-@@ -116,7 +137,11 @@ class SVGImageContext {
+@@ -110,7 +131,11 @@ class SVGImageContext {
     return contextPaintIsEqual && mViewportSize == aOther.mViewportSize &&
            mPreserveAspectRatio == aOther.mPreserveAspectRatio &&
            mColorScheme == aOther.mColorScheme &&
@@ -57,17 +57,17 @@ index b1f811989697966e30859610f4fc07579d0385ab..f6f4cd5a45fc49b416111d980fab4e61
   }
 
   bool operator!=(const SVGImageContext&) const = default;
-@@ -129,7 +154,8 @@ class SVGImageContext {
-     return HashGeneric(hash, mViewportSize.map(HashSize).valueOr(0),
-                        mPreserveAspectRatio.map(HashPAR).valueOr(0),
-                        mColorScheme.map(HashColorScheme).valueOr(0),
-                       HashLinkParameters(mLinkParameters));
-+                       HashLinkParameters(mLinkParameters), mZenBoostsAccent,
-+                       mZenBoostsComplementaryRotation, mZenBoostsInverted);
+@@ -123,7 +148,8 @@ class SVGImageContext {
+     return AddToHash(hash, mViewportSize.map(HashSize).valueOr(0),
+                      mPreserveAspectRatio.map(HashPAR).valueOr(0),
+                      mColorScheme.map(HashColorScheme).valueOr(0),
+-                     HashLinkParameters(mLinkParameters));
+                     HashLinkParameters(mLinkParameters), mZenBoostsAccent,
+                     mZenBoostsComplementaryRotation, mZenBoostsInverted);
   }
 
  private:
-@@ -167,6 +193,9 @@ class SVGImageContext {
+@@ -156,6 +182,9 @@ class SVGImageContext {
   Maybe<SVGPreserveAspectRatio> mPreserveAspectRatio;
   Maybe<ColorScheme> mColorScheme;
   StyleLinkParameters mLinkParameters;
--- a/src/services/sync/modules/service-sys-mjs.patch
+++ b/src/services/sync/modules/service-sys-mjs.patch
@@ -1,5 +1,5 @@
 diff --git a/services/sync/modules/service.sys.mjs b/services/sync/modules/service.sys.mjs
-index 4f4efe572909441abdd81909282936702c225621..81ab06a9414ed656b644a21b40b683f06a4f8dbf 100644
+index 4f4efe572909441abdd81909282936702c225621..2b47a2c9e97cf87641a0be9814f9a6be4d43f6ea 100644
 --- a/services/sync/modules/service.sys.mjs
 +++ b/services/sync/modules/service.sys.mjs
@@ -99,6 +99,10 @@ function getEngineModules() {
@@ -7,8 +7,8 @@ index 4f4efe572909441abdd81909282936702c225621..81ab06a9414ed656b644a21b40b683f0
     whenFalse: "ExtensionStorageEngineBridge",
   };
 +  result.Spaces = {
-+    module: "resource:///modules/zen/ZenWorkspacesSync.sys.mjs",
-+    symbol: "ZenWorkspacesEngine",
+    module: "resource:///modules/zen/ZenSpacesSync.sys.mjs",
+    symbol: "ZenSpacesSyncEngine",
 +  };
   return result;
 }
--- a/src/testing/xpcshell/runxpcshelltests-py.patch
+++ b/src/testing/xpcshell/runxpcshelltests-py.patch
@@ -0,0 +1,14 @@
+diff --git a/testing/xpcshell/runxpcshelltests.py b/testing/xpcshell/runxpcshelltests.py
+index 403401613189ffb758037850dc6bbb1d55f194ab..cad28e245155eb54775e551885532026e56c5fa9 100755
+--- a/testing/xpcshell/runxpcshelltests.py
+++ b/testing/xpcshell/runxpcshelltests.py
+@@ -2275,6 +2275,9 @@ class XPCShellTests:
+         appDirKey = None
+         if "appname" in self.mozInfo:
+             appDirKey = self.mozInfo["appname"] + "-appdir"
+            if appDirKey == "zen-appdir":
+                # Inherited manifests use firefox-appdir.
+                appDirKey = "firefox-appdir"
+ 
+         # We have to do this before we run tests that depend on having the node
+         # http/2 server.
--- a/src/toolkit/components/contextualidentity/ContextualIdentityService-sys-mjs.patch
+++ b/src/toolkit/components/contextualidentity/ContextualIdentityService-sys-mjs.patch
@@ -1,37 +0,0 @@
-diff --git a/toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs b/toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs
-index 5702ff28cc22206f5ce16584dac8a78d816562ce..3d08ecc97ce5995b30d8a4af0c33df329b428008 100644
--- a/toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs
-+++ b/toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs
-@@ -270,11 +270,29 @@ _ContextualIdentityService.prototype = {
-     });
-   },
- 
-  create(name, icon, color) {
-+  create(name, icon, color, id = null) {
-     this.ensureDataReady();
- 
-    // Retrieve the next userContextId available.
-    let userContextId = ++this._lastUserContextId;
-+    if (id !== null) {
-+      id = typeof id == "string" ? Number(id) : id;
-+      if (!Number.isSafeInteger(id) || id <= 0) {
-+        throw new Error(`Invalid userContextId '${id}'`);
-+      }
-+    }
-+
-+    let userContextId;
-+    if (
-+      id !== null &&
-+      !this._identities.some(identity => identity.userContextId === id)
-+    ) {
-+      userContextId = id;
-+      this._lastUserContextId = Math.max(
-+        this._lastUserContextId,
-+        userContextId
-+      );
-+    } else {
-+      userContextId = ++this._lastUserContextId;
-+    }
- 
-     // Throw an error if the next userContextId available is invalid (the one associated to
-     // MAX_USER_CONTEXT_ID is already reserved to "userContextIdInternal.webextStorageLocal", which
--- a/src/toolkit/content/widgets/moz-toggle/moz-toggle-tokens-css.patch
+++ b/src/toolkit/content/widgets/moz-toggle/moz-toggle-tokens-css.patch
@@ -1,5 +1,5 @@
 diff --git a/toolkit/content/widgets/moz-toggle/moz-toggle.tokens.css b/toolkit/content/widgets/moz-toggle/moz-toggle.tokens.css
-index 6247d7a3923a6fedd4ec9911aba309ce565cd498..744e670eccc936dde664aa07df3e87bdcafd5e48 100644
+index c0976c54418a28046802443931042bd285aefbde..2adb18d25edbb8aac4e396fcfc64a4a664607836 100644
 --- a/toolkit/content/widgets/moz-toggle/moz-toggle.tokens.css
 +++ b/toolkit/content/widgets/moz-toggle/moz-toggle.tokens.css
@@ -13,8 +13,8 @@
@@ -11,5 +11,5 @@ index 6247d7a3923a6fedd4ec9911aba309ce565cd498..744e670eccc936dde664aa07df3e87bd
 +    --toggle-background-color-pressed: var(--zen-primary-color);
 +    --toggle-background-color-pressed-hover: var(--zen-colors-hover-bg);
     --toggle-background-color-pressed-active: var(--color-accent-primary-active);
-     --toggle-border-color: var(--border-color-interactive);
+     --toggle-border-color: light-dark(var(--color-gray-70), var(--border-color-interactive));
     --toggle-border-color-hover: var(--toggle-border-color);
--- a/src/toolkit/content/widgets/panel-list/panel-list-mjs.patch
+++ b/src/toolkit/content/widgets/panel-list/panel-list-mjs.patch
@@ -0,0 +1,29 @@
+diff --git a/toolkit/content/widgets/panel-list/panel-list.mjs b/toolkit/content/widgets/panel-list/panel-list.mjs
+index 68ad2fafc8b31dfff541cf8381d9b9533e376d1c..fa62fec6bfb33338091fc06d3736fb76fd5c47c4 100644
+--- a/toolkit/content/widgets/panel-list/panel-list.mjs
+++ b/toolkit/content/widgets/panel-list/panel-list.mjs
+@@ -223,7 +223,12 @@ export class PanelList extends HTMLElement {
+     this.setAttribute("showing", "true");
+     // Tell the host element to hide any overflow in case the panel extends off
+     // the page before the alignment is set.
+-    hostElement.style.overflow = "hidden";
+    const hostHidesOverflow = !getComputedStyle(hostElement)
+      .overflow.split(" ")
+      .includes("visible");
+    if (!hostHidesOverflow) {
+      hostElement.style.overflow = "hidden";
+    }
+ 
+     // Wait for a layout flush, then find the bounds.
+     let {
+@@ -344,7 +349,9 @@ export class PanelList extends HTMLElement {
+       // Set the alignments and show the panel.
+       this.setAttribute("align", align);
+       this.setAttribute("valign", valign);
+-      hostElement.style.overflow = "";
+      if (!hostHidesOverflow) {
+        hostElement.style.overflow = "";
+      }
+       // Decide positioning based on where this panel will be rendered
+       const offsetParentIsBody =
+         this.supportsPopover() ||
--- a/src/widget/cocoa/nsCocoaWindow-h.patch
+++ b/src/widget/cocoa/nsCocoaWindow-h.patch
@@ -1,8 +1,8 @@
 diff --git a/widget/cocoa/nsCocoaWindow.h b/widget/cocoa/nsCocoaWindow.h
-index 312011c1c2ac41e78affecbdef25d72766a7c882..e5865c7d6259f0a3df48edf7a26b1b75a23cdb3a 100644
+index 22a2a7ef3a5e9257c8bb00ba6a55e8d39d2abbd9..6d8353fd11921585f7101f5717bdb3dd8f2a5eae 100644
 --- a/widget/cocoa/nsCocoaWindow.h
 +++ b/widget/cocoa/nsCocoaWindow.h
-@@ -462,6 +462,10 @@ class nsCocoaWindow final : public nsIWidget {
+@@ -461,6 +461,10 @@ class nsCocoaWindow final : public nsIWidget {
   void SetHideTitlebarSeparator(bool) override;
   bool IsMacTitlebarDirectionRTL() override;
   void SetCustomTitlebar(bool) override;
@@ -13,9 +13,9 @@ index 312011c1c2ac41e78affecbdef25d72766a7c882..e5865c7d6259f0a3df48edf7a26b1b75
   void UpdateThemeGeometries(
       const nsTArray<ThemeGeometry>& aThemeGeometries) override;
   void LockAspectRatio(bool aShouldLock) override;
-@@ -672,6 +676,7 @@ class nsCocoaWindow final : public nsIWidget {
-   bool mAspectRatioLocked = false;
-   bool mIsAlert = false;  // True if this is an non-native alert window.
+@@ -674,6 +678,7 @@ class nsCocoaWindow final : public nsIWidget {
+   // show (e.g. a window created by detaching a tab from a fullscreen window).
+   bool mIsInitialFullscreenSuppressed = false;
   bool mWasShown = false;
 +  bool mIsBrowserWindow = false;
 
--- a/src/widget/gtk/nsDragSessionSource-cpp.patch
+++ b/src/widget/gtk/nsDragSessionSource-cpp.patch
@@ -0,0 +1,29 @@
+diff --git a/widget/gtk/nsDragSessionSource.cpp b/widget/gtk/nsDragSessionSource.cpp
+index a5f67d700f8c80d513f08cc25405b57cf28a2a9a..58186470bcbb7b1eda34ee20a19e29d540ab052a 100644
+--- a/widget/gtk/nsDragSessionSource.cpp
+++ b/widget/gtk/nsDragSessionSource.cpp
+@@ -13,6 +13,7 @@
+ #include "mozilla/Services.h"
+ #include "mozilla/StaticPrefs_widget.h"
+ #include "mozilla/WidgetUtilsGtk.h"
+#include "mozilla/nsZenDragAndDrop.h"
+ #include "nsAppShell.h"
+ #include "nsArrayUtils.h"
+ #include "nsCRT.h"
+@@ -1196,11 +1197,15 @@ bool nsDragSessionSource::SetAlphaPixmap(SourceSurface* aSurface,
+       cairo_image_surface_get_stride(surf), SurfaceFormat::B8G8R8A8);
+   if (!dt) return false;
+ 
+  auto drag_translucency = DRAG_IMAGE_ALPHA_LEVEL;
+  if (auto zenDragAndDrop = zen::nsZenDragAndDrop::GetZenDragAndDropInstance()) {
+    drag_translucency = zenDragAndDrop->GetDragImageOpacity();
+  }
+   dt->ClearRect(Rect(0, 0, dragRect.width, dragRect.height));
+   dt->DrawSurface(
+       aSurface, Rect(0, 0, dragRect.width, dragRect.height),
+       Rect(0, 0, dragRect.width, dragRect.height), DrawSurfaceOptions(),
+-      DrawOptions(DRAG_IMAGE_ALPHA_LEVEL, CompositionOp::OP_SOURCE));
+      DrawOptions(drag_translucency, CompositionOp::OP_SOURCE));
+ 
+   cairo_surface_mark_dirty(surf);
+   cairo_surface_set_device_offset(surf, -aXOffset, -aYOffset);
--- a/src/zen/boosts/zen-boost-editor.inc.xhtml
+++ b/src/zen/boosts/zen-boost-editor.inc.xhtml
@@ -49,9 +49,9 @@
    <vbox flex="1" id="zen-boost-filter-wrapper">
      <hbox class="zen-boost-color-picker-gradient zen-boost-panel-disabled">
        <button data-l10n-id="zen-boost-magic-theme" id="zen-boost-magic-theme" class="subviewbutton mod-button"></button>
-        <html:div id="zen-boost-color-picker-dot-primary" class="zen-boost-color-picker-dot"></html:div>
-        <html:div id="zen-boost-color-picker-dot-secondary" class="zen-boost-color-picker-dot"></html:div>
-        <html:div class="zen-boost-color-picker-circle"></html:div>
+        <html:div id="zen-boost-color-picker-dot-primary" class="zen-boost-color-picker-dot no-squircles"></html:div>
+        <html:div id="zen-boost-color-picker-dot-secondary" class="zen-boost-color-picker-dot no-squircles"></html:div>
+        <html:div class="zen-boost-color-picker-circle no-squircles"></html:div>
      </hbox>

      <hbox flex="1" id="zen-boost-toolbar-wrapper-colors">
--- a/src/zen/boosts/zen-boosts.css
+++ b/src/zen/boosts/zen-boosts.css
@@ -194,7 +194,8 @@ body {
  max-height: 40px;
  align-items: center;
  background-color: var(--zen-boosts-secondary-background);
-  border: solid 1px var(--zen-boosts-primary-border-color);
+  border: solid 1px transparent;
+  border-bottom-color: var(--zen-boosts-primary-border-color);

  @media (-moz-windows-mica) {
    background-color: var(--zen-boosts-mica-background);
--- a/src/zen/common/modules/ZenStartup.mjs
+++ b/src/zen/common/modules/ZenStartup.mjs
@@ -4,6 +4,7 @@

 import checkForZenUpdates, {
  createWindowUpdateAnimation,
+  playWindowSweepAnimation,
 } from "chrome://browser/content/ZenUpdates.mjs";

 class ZenStartup {
@@ -195,6 +196,14 @@ class ZenStartup {
    checkForZenUpdates();
    return await createWindowUpdateAnimation();
  }
+
+  /**
+   * Entry point for privileged modules (e.g. the sync applier) to play the
+   * update sweep animation in this window.
+   */
+  playWindowSweepAnimation() {
+    return playWindowSweepAnimation();
+  }
 }

 window.gZenStartup = new ZenStartup();
--- a/src/zen/common/modules/ZenUIManager.mjs
+++ b/src/zen/common/modules/ZenUIManager.mjs
@@ -493,6 +493,13 @@ window.gZenUIManager = {
  _clearTimeout: null,
  _lastTab: null,

+  _urlbarSessionCounter: 0,
+  _urlbarOwner: null,
+
+  _isOwner(closeSeq) {
+    return this._urlbarOwner === closeSeq;
+  },
+
  // Check if browser elements are in a valid state for tab operations
  _validateBrowserState() {
    // Check if browser window is still open
@@ -517,8 +524,15 @@ window.gZenUIManager = {
    werePassedURL,
    searchClipboard,
    where,
-    overridePreferance = false
+    overridePreferance = false,
+    closeToken = {}
  ) {
+    // Keep this here. It's better to make sure every
+    // call has a different token rather then forgetting
+    // to increment it in one of the early returns.
+    const closeSeq = ++this._urlbarSessionCounter;
+    closeToken.id = closeSeq;
+
    // Validate browser state first
    if (!this._validateBrowserState()) {
      console.warn("Browser state invalid for new tab operation");
@@ -542,7 +556,13 @@ window.gZenUIManager = {

    // Close the new tab popup on cmd/ctrl + t
    if (!overridePreferance && gURLBar.hasAttribute("zen-newtab")) {
-      this.handleUrlbarClose();
+      // The _zenHandleUrlbarClose holds a token in it's closure.
+      // Call that instead.
+      if (gURLBar._zenHandleUrlbarClose) {
+        gURLBar._zenHandleUrlbarClose();
+      } else {
+        this.handleUrlbarClose(closeSeq);
+      }
      return true;
    }

@@ -568,7 +588,9 @@ window.gZenUIManager = {
    this._prevUrlbarLabel = gURLBar._untrimmedValue || "";

    // Set up URL bar for new tab
-    gURLBar._zenHandleUrlbarClose = this.handleUrlbarClose.bind(this);
+    gURLBar._zenHandleUrlbarClose = (onSwitch, onElementPicked) =>
+      this.handleUrlbarClose(closeSeq, onSwitch, onElementPicked);
+    this._urlbarOwner = closeSeq;
    gURLBar.setAttribute("zen-newtab", true);

    // Update newtab buttons
@@ -582,18 +604,33 @@ window.gZenUIManager = {
      document.getElementById("Browser:OpenLocation").doCommand();
    } catch (e) {
      console.error("Error opening location in new tab:", e);
-      this.handleUrlbarClose(false);
+      this.handleUrlbarClose(closeSeq, false, false);
      return false;
    }
    return true;
  },

+  /**
+   * Check whether the closeToken given by handleNewTab
+   * corresponds to a close event.
+   *
+   * @param {object} closeToken - Token previously passed to handleNewTab.
+   * @param {CustomEvent} event - A ZenURLBarClosed event.
+   * @returns {boolean}
+   */
+  matchesCloseToken(closeToken, event) {
+    return (
+      typeof closeToken?.id === "number" &&
+      event?.detail?.closeSeq === closeToken.id
+    );
+  },
+
  clearUrlbarData() {
    this._prevUrlbarLabel = null;
    this._lastSearch = "";
  },

-  handleUrlbarClose(onSwitch = false, onElementPicked = false) {
+  handleUrlbarClose(closeSeq, onSwitch = false, onElementPicked = false) {
    // Validate browser state first
    if (!this._validateBrowserState()) {
      console.warn("Browser state invalid for URL bar close operation");
@@ -607,59 +644,69 @@ window.gZenUIManager = {

    const isFocusedBefore = gURLBar.focused;
    setTimeout(() => {
-      // We use this attribute on Tabbrowser::addTab
-      gURLBar.removeAttribute("zen-newtab");
+      /* If someone else opened the url bar in the meantime don't be
+       * stingy and leave it open for them.*/
+      if (this._isOwner(closeSeq)) {
+        // We use this attribute on Tabbrowser::addTab
+        gURLBar.removeAttribute("zen-newtab");

-      // Safely restore tab visual state with proper validation
-      if (
-        this._lastTab &&
-        !this._lastTab.closing &&
-        this._lastTab.documentGlobal &&
-        !this._lastTab.documentGlobal.closed &&
-        gBrowser.selectedTab === this._lastTab
-      ) {
-        this._lastTab._visuallySelected = true;
-        this._lastTab = null;
-      }
-
-      // Reset newtab buttons
-      for (const button of this.newtabButtons) {
-        button.removeAttribute("in-urlbar");
-      }
-
-      // Handle search data
-      if (onSwitch) {
-        this.clearUrlbarData();
-      } else {
-        this._lastSearch = gURLBar._untrimmedValue || "";
-
-        if (this._clearTimeout) {
-          clearTimeout(this._clearTimeout);
+        // Safely restore tab visual state with proper validation
+        if (
+          this._lastTab &&
+          !this._lastTab.closing &&
+          this._lastTab.documentGlobal &&
+          !this._lastTab.documentGlobal.closed &&
+          gBrowser.selectedTab === this._lastTab
+        ) {
+          this._lastTab._visuallySelected = true;
+          this._lastTab = null;
        }

-        this._clearTimeout = setTimeout(() => {
+        // Reset newtab buttons
+        for (const button of this.newtabButtons) {
+          button.removeAttribute("in-urlbar");
+        }
+
+        // Handle search data
+        if (onSwitch) {
          this.clearUrlbarData();
-        }, this.urlbarWaitToClear);
-      }
+        } else {
+          this._lastSearch = gURLBar._untrimmedValue || "";

-      // Safely restore URL bar state with proper validation
-      if (this._prevUrlbarLabel) {
-        gURLBar.setURI({
-          uri: this._prevUrlbarLabel,
-          dueToTabSwitch: onSwitch,
-          isSameDocument: !onSwitch,
-        });
-      }
+          if (this._clearTimeout) {
+            clearTimeout(this._clearTimeout);
+          }

-      gURLBar.handleRevert();
+          this._clearTimeout = setTimeout(() => {
+            this.clearUrlbarData();
+          }, this.urlbarWaitToClear);
+        }
+
+        // Safely restore URL bar state with proper validation
+        if (this._prevUrlbarLabel) {
+          gURLBar.setURI({
+            uri: this._prevUrlbarLabel,
+            dueToTabSwitch: onSwitch,
+            isSameDocument: !onSwitch,
+          });
+        }
+
+        gURLBar.handleRevert();
+      }

      if (isFocusedBefore) {
        setTimeout(() => {
          window.dispatchEvent(
            new CustomEvent("ZenURLBarClosed", {
-              detail: { onSwitch, onElementPicked },
+              detail: { onSwitch, onElementPicked, closeSeq },
            })
          );
+
+          if (!this._isOwner(closeSeq)) {
+            return;
+          }
+          this._urlbarOwner = null;
+
          gURLBar.view.close({ elementPicked: onElementPicked });
          gURLBar.updateTextOverflow();

@@ -683,6 +730,8 @@ window.gZenUIManager = {
            }
          }
        }, 0);
+      } else if (this._isOwner(closeSeq)) {
+        this._urlbarOwner = null;
      }
    }, 0);
  },
@@ -1233,7 +1282,7 @@ window.gZenVerticalTabsManager = {
        if (!this._hasSetSingleToolbar) {
          height = AppConstants.platform == "macosx" ? 34 : 32;
        } else if (!gURLBar.hasAttribute("breakout-extend")) {
-          height = 38;
+          height = 36;
        }
        if (typeof height !== "undefined") {
          gURLBar.style.setProperty("--urlbar-height", `${height}px`);
@@ -1299,18 +1348,21 @@ window.gZenVerticalTabsManager = {
        document.documentElement.removeAttribute("zen-right-side");
      }

-      delete this._hadSidebarCollapse;
-      if (isSidebarExpanded) {
-        this._hadSidebarCollapse = !document.documentElement.hasAttribute(
-          "zen-sidebar-expanded"
-        );
-        this.navigatorToolbox.setAttribute("zen-sidebar-expanded", "true");
-        document.documentElement.setAttribute("zen-sidebar-expanded", "true");
-        gBrowser.tabContainer.setAttribute("expanded", "true");
-      } else {
-        this.navigatorToolbox.removeAttribute("zen-sidebar-expanded");
-        document.documentElement.removeAttribute("zen-sidebar-expanded");
-        gBrowser.tabContainer.removeAttribute("expanded");
+      const wasSidebarExpanded = document.documentElement.hasAttribute(
+        "zen-sidebar-expanded"
+      );
+      if (isSidebarExpanded !== wasSidebarExpanded) {
+        delete this._hadSidebarCollapse;
+        if (isSidebarExpanded) {
+          this._hadSidebarCollapse = true;
+          this.navigatorToolbox.setAttribute("zen-sidebar-expanded", "true");
+          document.documentElement.setAttribute("zen-sidebar-expanded", "true");
+          gBrowser.tabContainer.setAttribute("expanded", "true");
+        } else {
+          this.navigatorToolbox.removeAttribute("zen-sidebar-expanded");
+          document.documentElement.removeAttribute("zen-sidebar-expanded");
+          gBrowser.tabContainer.removeAttribute("expanded");
+        }
      }

      const appContentNavbarContaienr = document.getElementById(
--- a/src/zen/common/modules/ZenUpdates.mjs
+++ b/src/zen/common/modules/ZenUpdates.mjs
@@ -61,6 +61,14 @@ export async function createWindowUpdateAnimation() {
    return;
  }
  Services.prefs.setStringPref(ZEN_BUILD_ID_PREF, appID);
+  await playWindowSweepAnimation();
+}
+
+/**
+ * Plays the full-window sweep shown after updates. Also used the first
+ * time incoming sync data is applied on this profile.
+ */
+export async function playWindowSweepAnimation() {
  await gZenWorkspaces.promiseInitialized;
  const appWrapper = document.getElementById("zen-main-app-wrapper");
  const element = document.createElement("div");
--- a/src/zen/common/styles/zen-omnibox.css
+++ b/src/zen/common/styles/zen-omnibox.css
@@ -20,9 +20,9 @@
  --urlbarview-separator-color: light-dark(hsl(0, 0%, 80%), hsl(0, 0%, 20%));
  --urlbarview-background-color-hover: var(--toolbarbutton-hover-background);
  border-radius: calc(var(--toolbarbutton-border-radius) - 2px);
-  height: var(--urlbar-height);
  --urlbarView-results-padding: 10px !important;
  --urlbar-container-height: 48px !important;
+  --urlbar-input-container-border: none;

  --urlbar-margin-inline: 5px;
  --urlbar-container-padding: 4px;
@@ -326,6 +326,7 @@
    order: 2;
  }

+  /* stylelint-disable-next-line stylelint-plugin-mozilla/no-has-selector */
  #notification-popup-box:not([open]):not(:has(> [showing="true"])) {
    margin-inline-start: calc(-10px - 2 * var(--urlbar-icon-padding));
    opacity: 0;
@@ -487,6 +488,7 @@
  translate: -50% 0%;
  left: 50% !important;

+  /* stylelint-disable-next-line stylelint-plugin-mozilla/no-has-selector */
  #urlbar-container:has(&) {
    border-radius: var(--border-radius-medium);
    background: var(--toolbarbutton-hover-background);
@@ -633,6 +635,7 @@

 #urlbar-label-box,
 #urlbar-search-mode-indicator {
+  --urlbar-basic-component-size: 18px;
  background-color: color-mix(in srgb, var(--zen-primary-color) 50%, light-dark(rgba(0, 0, 0, 0.5), rgba(255, 255, 255, 0.2)) 50%) !important;
  color: white;
  padding: 4px 8px;
@@ -717,6 +720,10 @@
  display: none;
 }

+.urlbarView {
+  overflow: visible;
+}
+
 #urlbar-search-mode-indicator-title {
  font-weight: 600;
  padding: 0;
--- a/src/zen/common/styles/zen-popup.css
+++ b/src/zen/common/styles/zen-popup.css
@@ -335,7 +335,7 @@ menuseparator {
    gap: 8px;
    z-index: 1000;
    padding: var(--zen-toast-padding);
-    border-radius: 10px;
+    border-radius: 14px;
    background: linear-gradient(to bottom, var(--zen-primary-color) -40%, color-mix(in srgb, var(--zen-primary-color), #0f0f0f 20%));
    box-shadow: light-dark(rgba(0, 0, 0, 0.1), rgba(0, 0, 0, 0.4)) 0 0 22px 2px;
    border: none;
@@ -374,7 +374,7 @@ menuseparator {
      min-width: unset !important;
      min-height: 28px;
      margin: 0 !important;
-      border-radius: 6px !important;
+      border-radius: 10px !important;
      border-top: 2px solid light-dark(transparent, rgba(255, 255, 255, 0.1));
      color: light-dark(rgba(0, 0, 0, 0.8), rgba(255, 255, 255, 0.8)) !important;
      box-shadow: 0 0 1px 1px rgba(0, 0, 0, 0.05);
--- a/src/zen/common/styles/zen-sidebar-notification.css
+++ b/src/zen/common/styles/zen-sidebar-notification.css
@@ -78,13 +78,13 @@
 }

 .zen-sidebar-notification-progress {
-  height: 2px;
+  height: 1px;
  overflow: hidden;
  transform: translateY(-1px);

  & .zen-sidebar-notification-progress-bar {
    height: 100%;
-    background: light-dark(color-mix(in srgb, var(--zen-primary-color) 50%, black), color-mix(in srgb, var(--zen-colors-primary) 15%, #ebebeb));
+    background: light-dark(color-mix(in srgb, var(--zen-primary-color) 50%, black), color-mix(in srgb, var(--zen-colors-primary) 15%, transparent 10%, #6b6b6b));
    transform-origin: left center;
  }
 }
--- a/src/zen/common/styles/zen-single-components.css
+++ b/src/zen/common/styles/zen-single-components.css
@@ -185,7 +185,7 @@
 .toolbarbutton-1:not(#tabs-newtab-button),
 .urlbar-page-action,
 .identity-box-button {
-  --tab-border-radius: 6px;
+  --tab-border-radius: 8px;
  --toolbarbutton-border-radius: var(--tab-border-radius);
  --toolbarbutton-padding-inner: 6px;
  --toolbarbutton-padding-outer: 1px;
@@ -502,11 +502,13 @@
      opacity 0.12s ease-in-out;
  }

+  /* stylelint-disable-next-line stylelint-plugin-mozilla/no-has-selector */
  .permission-popup-permission-item:hover &::before,
  .permission-popup-boost-item:hover:not(:has(.zen-permission-popup-boost-editor-button:hover)) &::before {
    transform: scale(1.05);
  }

+  /* stylelint-disable-next-line stylelint-plugin-mozilla/no-has-selector */
  .permission-popup-permission-item:active:hover &::before,
  .permission-popup-boost-item:active:hover:not(:has(.zen-permission-popup-boost-editor-button:hover)) &::before {
    transform: scale(0.95);
@@ -601,6 +603,7 @@
      position: absolute;
      width: 100%;
      height: 100%;
+
      @media (-moz-platform: macos) {
        background: linear-gradient(to bottom, light-dark(rgb(255, 255, 255), rgb(34, 34, 34)), light-dark(rgb(246, 246, 246), rgb(21, 21, 21)));

--- a/src/zen/common/styles/zen-theme.css
+++ b/src/zen/common/styles/zen-theme.css
@@ -92,7 +92,11 @@
  --in-content-accent-color-active: currentColor !important;

  /* This is like the secondary button */
-  --in-content-button-background: transparent !important;
+  --in-content-button-background: color-mix(
+    in srgb,
+    currentColor,
+    transparent 90%
+  ) !important;
  --in-content-button-text-color: var(--zen-secondary-btn-color) !important;
  --in-content-button-background-hover: color-mix(
    in srgb,
@@ -213,6 +217,16 @@
  --toolbarbutton-border-radius: 6px;
  --urlbar-margin-inline: 1px !important;

+  --zen-squircle-value: 1.3;
+
+  @media (-moz-platform: windows) {
+    --zen-squircle-value: 2.1;
+  }
+
+  @media (-moz-platform: linux) {
+    --zen-squircle-value: 1.2;
+  }
+
  --tab-icon-overlay-stroke: light-dark(white, black) !important;
  --tab-close-button-padding: 4px !important;

@@ -344,3 +358,11 @@
 }

 %include zen-buttons.css
+
+@media (-moz-pref('layout.css.corner-shape.enabled')) {
+  *:not(.no-squircles),
+  .zen-squircle-before::before,
+  .zen-squircle-after::after {
+    corner-shape: superellipse(var(--zen-squircle-value));
+  }
+}
--- a/src/zen/compact-mode/ZenCompactMode.mjs
+++ b/src/zen/compact-mode/ZenCompactMode.mjs
@@ -832,8 +832,9 @@ window.gZenCompactModeManager = {

      const onLeave = event => {
        if (AppConstants.platform == "macosx") {
-          const buttonRect =
-            gZenVerticalTabsManager.actualWindowButtons.getBoundingClientRect();
+          const buttonRect = window.windowUtils.getBoundsWithoutFlushing(
+            gZenVerticalTabsManager.actualWindowButtons
+          );
          const MAC_WINDOW_BUTTONS_X_BORDER = buttonRect.width + buttonRect.x;
          const MAC_WINDOW_BUTTONS_Y_BORDER = buttonRect.height + buttonRect.y;
          if (
--- a/src/zen/compact-mode/zen-compact-mode.css
+++ b/src/zen/compact-mode/zen-compact-mode.css
@@ -29,7 +29,7 @@
  &,
  &::before,
  &::after {
-    border-radius: calc(var(--zen-native-inner-radius) - var(--zen-compact-mode-no-padding-radius-fix, 0px));
+    border-radius: calc((var(--zen-native-inner-radius) - var(--zen-compact-mode-no-padding-radius-fix, 0px)) * var(--zen-squircle-value));
  }
 }

--- a/src/zen/drag-and-drop/ZenDragAndDrop.js
+++ b/src/zen/drag-and-drop/ZenDragAndDrop.js
@@ -183,10 +183,10 @@
          if (tabClone.hasAttribute("visuallyselected")) {
            tabClone.style.transform = "translate(-50%, -50%)";
          }
-        } else if (AppConstants.platform !== "macosx" && !tab.isZenFolder) {
-          // On windows and linux, we still don't add some extra opaqueness
-          // for the tab to be more visible. This is a hacky workaround.
-          // TODO: Make windows and linux DnD use nsZenDragAndDrop::mDragImageOpacity
+        } else if (AppConstants.platform == "win" && !tab.isZenFolder) {
+          // On windows, the shell applies its own translucency to the drag
+          // image which we can't control, so force some extra contrast for
+          // the tab to be more visible. This is a hacky workaround.
          tabClone.style.colorScheme = "light";
          tabClone.style.setProperty("--tab-selected-textcolor", "black");
        }
--- a/src/zen/folders/ZenFolder.mjs
+++ b/src/zen/folders/ZenFolder.mjs
@@ -12,7 +12,7 @@ export class nsZenFolder extends MozTabbrowserTabGroup {
  #initialized = false;

  static markup = `
-      <hbox class="tab-group-label-container zen-drop-target" pack="center">
+      <hbox class="tab-group-label-container zen-squircle-before zen-drop-target" pack="center">
        <html:div class="tab-group-folder-icon"/>
        <label class="tab-group-label" role="button"/>
        <image class="tab-reset-button reset-icon" role="button" keyNav="false" data-l10n-id="zen-folders-unload-all-tooltip"/>
--- a/src/zen/glance/zen-glance.css
+++ b/src/zen/glance/zen-glance.css
@@ -41,11 +41,11 @@

    &:hover {
      background: light-dark(rgb(41, 41, 41), rgb(204, 204, 204));
-      scale: 1.05;
+      scale: 1.02;
    }

    &:hover:active {
-      scale: 0.95;
+      scale: 0.98;
    }

    & label {
--- a/src/zen/glance/zen-glance.inc.xhtml
+++ b/src/zen/glance/zen-glance.inc.xhtml
@@ -4,8 +4,8 @@

 <html:template id="zen-glance-sidebar-template">
  <vbox class="zen-glance-sidebar-container">
-    <toolbarbutton class="zen-glance-sidebar-close toolbarbutton-1" command="cmd_zenGlanceClose" data-l10n-id="zen-general-confirm" />
-    <toolbarbutton class="zen-glance-sidebar-open toolbarbutton-1" command="cmd_zenGlanceExpand" />
-    <toolbarbutton class="zen-glance-sidebar-split toolbarbutton-1" command="cmd_zenGlanceSplit" />
+    <toolbarbutton class="no-squircles zen-glance-sidebar-close toolbarbutton-1" command="cmd_zenGlanceClose" data-l10n-id="zen-general-confirm" />
+    <toolbarbutton class="no-squircles zen-glance-sidebar-open toolbarbutton-1" command="cmd_zenGlanceExpand" />
+    <toolbarbutton class="no-squircles zen-glance-sidebar-split toolbarbutton-1" command="cmd_zenGlanceSplit" />
  </vbox>
 </html:template>
--- a/src/zen/live-folders/ZenLiveFoldersManager.sys.mjs
+++ b/src/zen/live-folders/ZenLiveFoldersManager.sys.mjs
@@ -200,6 +200,50 @@ class nsZenLiveFoldersManager {
    return this.liveFolders.get(id);
  }

+  /**
+   * Returns the provider config needed to recreate this live folder on
+   * another device, or null for non-live folders. Fetch bookkeeping fields
+   * are stripped since they are device-local.
+   *
+   * @param {string} id - The folder ID.
+   */
+  getSyncableFolderData(id) {
+    const liveFolder = this.liveFolders.get(id);
+    if (!liveFolder) {
+      return null;
+    }
+    const state = { ...liveFolder.serialize().state };
+    delete state.lastFetched;
+    delete state.lastErrorId;
+    return { type: liveFolder.constructor.type, state };
+  }
+
+  /**
+   * Registers a live folder provider for a folder that arrived from
+   * Firefox Sync. The folder element must already exist.
+   *
+   * @param {string} id - The folder ID.
+   * @param {{ type: string, state: object }} config - Synced provider config.
+   */
+  async adoptSyncedFolder(id, { type, state } = {}) {
+    await this.stateRestored.promise;
+    if (this.liveFolders.has(id)) {
+      return;
+    }
+    const ProviderClass = this.registry.get(type);
+    if (!ProviderClass || !state) {
+      return;
+    }
+    const liveFolder = new ProviderClass({
+      id,
+      state: this.#applyDefaultStateValues({ ...state }),
+      manager: this,
+    });
+    this.liveFolders.set(id, liveFolder);
+    liveFolder.start();
+    this.saveState();
+  }
+
  async createFolder(type) {
    const [provider, providerType] = type.split(":");
    let ProviderClass = this.registry.get(provider);
@@ -324,7 +368,7 @@ class nsZenLiveFoldersManager {
              },
            ],
            content: {
-              width: "310px",
+              width: "312px",
              position: "callout",
              title_logo: {
                imageURL: icon,
@@ -619,6 +663,7 @@ class nsZenLiveFoldersManager {
  async #restoreState() {
    let data = await this.#readStateFromDisk();
    if (!Array.isArray(data)) {
+      this.stateRestored.resolve();
      return;
    }

--- a/src/zen/media/ZenMediaController.mjs
+++ b/src/zen/media/ZenMediaController.mjs
@@ -346,7 +346,7 @@ class ZenMediaCard {

  onToggle() {
    if (this.controller?.isPlaying) {
-      this.controller.pause();
+      this.controller.pause("user");
    } else {
      this.controller?.play();
    }
@@ -365,7 +365,7 @@ class ZenMediaCard {
  }

  onSeekDrag(event) {
-    this.controller?.pause();
+    this.controller?.pause("user");
    const newTime = (event.target.value / 100) * this.duration;
    this.currentTimeEl.textContent = this.formatSecondsToTime(newTime);
  }
@@ -408,7 +408,7 @@ class ZenMediaCard {

  onClose() {
    if (this.controller) {
-      this.controller.pause();
+      this.controller.pause("user");
    } else {
      const webRTC =
        this.browser.browsingContext.currentWindowGlobal.getActor("WebRTC");
--- a/src/zen/sessionstore/ZenSessionManager.sys.mjs
+++ b/src/zen/sessionstore/ZenSessionManager.sys.mjs
@@ -10,7 +10,6 @@ const lazy = {};
 ChromeUtils.defineESModuleGetters(lazy, {
  ZenLiveFoldersManager:
    "resource:///modules/zen/ZenLiveFoldersManager.sys.mjs",
-  ZenSyncStore: "resource:///modules/zen/ZenSyncManager.sys.mjs",
  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
  SessionStartup: "resource:///modules/sessionstore/SessionStartup.sys.mjs",
@@ -611,7 +610,9 @@ export class nsZenSessionManager {
      }
    );
    this.#collectWindowData(windows);
-    lazy.ZenSyncStore.notifyAboutChanges();
+    // Let interested consumers (e.g. Firefox Sync) know fresh sidebar data
+    // is available, without this module knowing anything about them.
+    Services.obs.notifyObservers(null, "zen-sidebar-data-collected");
    // This would save the data to disk asynchronously or when quitting the app.
    let sidebar = this.#sidebarWithoutCloning;
    this.#file.data = sidebar;
--- a/src/zen/sessionstore/ZenWindowSync.sys.mjs
+++ b/src/zen/sessionstore/ZenWindowSync.sys.mjs
@@ -606,7 +606,9 @@ class nsZenWindowSync {
    if (isTab) {
      if (originalIsEssential !== targetIsEssential) {
        if (originalIsEssential) {
-          gZenPinnedTabManager.addToEssentials(aTargetItem);
+          gZenPinnedTabManager.addToEssentials(aTargetItem, {
+            replicating: true,
+          });
        } else {
          gZenPinnedTabManager.removeEssentials(
            aTargetItem,
@@ -1232,7 +1234,7 @@ class nsZenWindowSync {
      activeIndex = Math.min(activeIndex, entries.length - 1);
      activeIndex = Math.max(activeIndex, 0);
      let entryToUse = (entries[activeIndex] || entries[0]) ?? null;
-      this.#setPinnedInitialState(
+      this.setPinnedInitialState(
        aTab,
        { url: entryToUse?.url, title: entryToUse?.title },
        image
@@ -1250,14 +1252,22 @@ class nsZenWindowSync {
   */
  setPinnedUrl(aTab, aUrl, aImage) {
    this.log(`Setting pinned url for tab ${aTab.id}`);
-    this.#setPinnedInitialState(
+    this.setPinnedInitialState(
      aTab,
      { url: aUrl, title: aTab.zenStaticLabel },
      aImage
    );
  }

-  #setPinnedInitialState(aTab, aEntry, aImage) {
+  /**
+   * Sets the pinned initial state (canonical entry and icon) for a tab's
+   * instances across all windows.
+   *
+   * @param {object} aTab - Any window's instance of the tab.
+   * @param {object} aEntry - The canonical { url, title } entry.
+   * @param {string} [aImage] - Optional icon to store.
+   */
+  setPinnedInitialState(aTab, aEntry, aImage) {
    const initialState = { entry: aEntry, image: aImage };
    this.#runOnAllWindows(null, win => {
      const targetTab = this.getItemFromWindow(win, aTab.id);
@@ -1362,7 +1372,9 @@ class nsZenWindowSync {
      return;
    }
    tab._zenContentsVisible = true;
-    tab.id = this.#newTabSyncId;
+    if (!tab.id) {
+      tab.id = this.#newTabSyncId;
+    }
    if (lazy.gSyncOnlyPinnedTabs && !tab.pinned) {
      return;
    }
--- a/src/zen/space-routing/ZenSpaceRoutingManager.sys.mjs
+++ b/src/zen/space-routing/ZenSpaceRoutingManager.sys.mjs
@@ -27,7 +27,7 @@ class nsZenSpaceRoutingManager {
    const element = window.MozXULElement.parseXULToFragment(`
        <menuseparator/>
        <menuitem id="context_zen-add-domain-to-routing"
-                  data-lazy-l10n-id="tab-context-zen-add-domain-to-sr"
+                  data-l10n-id="tab-context-zen-add-domain-to-sr"
                  data-l10n-args='{"tabCount": 1}'/>
      `);
    window.document.getElementById("context_undoCloseTab").after(element);
--- a/src/zen/spaces/ZenSpace.mjs
+++ b/src/zen/spaces/ZenSpace.mjs
@@ -52,7 +52,7 @@ export class nsZenWorkspace extends MozXULElement {

  static get markup() {
    return `
-        <vbox class="zen-workspace-tabs-section zen-current-workspace-indicator zen-drop-target" flex="1" context="zenWorkspaceMoreActions">
+        <vbox class="zen-workspace-tabs-section zen-current-workspace-indicator zen-squircle-before zen-drop-target" flex="1" context="zenWorkspaceMoreActions">
          <stack class="zen-current-workspace-indicator-stack">
            <image class="zen-current-workspace-indicator-chevron" />
            <hbox class="zen-current-workspace-indicator-icon" />
--- a/src/zen/spaces/ZenSpaceManager.mjs
+++ b/src/zen/spaces/ZenSpaceManager.mjs
@@ -11,7 +11,6 @@ const lazy = {};

 ChromeUtils.defineESModuleGetters(lazy, {
  ZenSessionStore: "resource:///modules/zen/ZenSessionManager.sys.mjs",
-  ZenSyncStore: "resource:///modules/zen/ZenSyncManager.sys.mjs",
 });

 ChromeUtils.defineLazyGetter(lazy, "browserBackgroundElement", () => {
@@ -157,11 +156,28 @@ class nsZenWorkspaces {
        this._invalidateBookmarkContainers();
      };
      Services.obs.addObserver(observerFunction, "workspace-bookmarks-updated");
+      const onContainerDeleted = subject => {
+        const userContextId = subject?.wrappedJSObject?.userContextId;
+        for (const workspace of this.getWorkspaces()) {
+          if (workspace.containerTabId === userContextId) {
+            workspace.containerTabId = 0;
+            this.saveWorkspace(workspace);
+          }
+        }
+      };
+      Services.obs.addObserver(
+        onContainerDeleted,
+        "contextual-identity-deleted"
+      );
      window.addEventListener("unload", () => {
        Services.obs.removeObserver(
          observerFunction,
          "workspace-bookmarks-updated"
        );
+        Services.obs.removeObserver(
+          onContainerDeleted,
+          "contextual-identity-deleted"
+        );
      });
    }
  }
@@ -173,63 +189,6 @@ class nsZenWorkspaces {
    }
  }

-  /**
-   * Applies live sync changes: updates workspace cache, removes deleted items,
-   * then creates/updates pulled items.
-   *
-   * @param {{ spaces: Array}} pulled  Reconcile-pulled items.
-   * @param {{ spaces: Array}} removals  Items to remove.
-   */
-  async _applySyncChanges(pulled, removals = {}) {
-    if (!this.shouldHaveWorkspaces || this.privateWindowOrDisabled) {
-      return;
-    }
-    await this.promiseInitialized;
-
-    // 1. Update workspace cache (remove deleted, merge pulled)
-    const removedSpaceIds = new Set((removals.spaces || []).map(s => s.uuid));
-    if (removedSpaceIds.size || pulled.spaces?.length) {
-      const localMap = new Map(
-        this.getWorkspaces()
-          .filter(w => !removedSpaceIds.has(w.uuid))
-          .map(w => [w.uuid, w])
-      );
-      for (const space of pulled.spaces || []) {
-        if (!space?.uuid) {
-          continue;
-        }
-        const existing = localMap.get(space.uuid);
-        localMap.set(space.uuid, existing ? { ...existing, ...space } : space);
-      }
-      await this.propagateWorkspaces(
-        this.#getOrderedWorkspacesByPosition(Array.from(localMap.values()))
-      );
-      this.#propagateWorkspaceData();
-    }
-  }
-
-  #getOrderedWorkspacesByPosition(workspaces) {
-    return [...workspaces]
-      .map((workspace, index) => ({ workspace, index }))
-      .sort((a, b) => {
-        const aPosition =
-          typeof a.workspace.position === "number"
-            ? a.workspace.position
-            : a.index;
-        const bPosition =
-          typeof b.workspace.position === "number"
-            ? b.workspace.position
-            : b.index;
-        return aPosition - bPosition || a.index - b.index;
-      })
-      .map(({ workspace }) => {
-        // strip the position property that comes from pulled workspaces
-        const rest = { ...workspace };
-        delete rest.position;
-        return rest;
-      });
-  }
-
  #afterLoadInit() {
    const onResize = (...args) => {
      requestAnimationFrame(() => {
@@ -862,13 +821,6 @@ class nsZenWorkspaces {
    })();
  }

-  #markWorkspaceChanged(workspaceId) {
-    lazy.ZenSyncStore.markItemChanged({
-      type: "space",
-      id: workspaceId,
-    });
-  }
-
  async selectStartPage() {
    if (!this.workspaceEnabled || gZenUIManager.testingEnabled) {
      return;
@@ -1297,8 +1249,6 @@ class nsZenWorkspaces {
    } else {
      workspacesData.push(workspaceData);
    }
-    // mark item as changed for sync
-    this.#markWorkspaceChanged(workspaceData.uuid);

    this.#propagateWorkspaceData();
  }
@@ -1307,9 +1257,6 @@ class nsZenWorkspaces {
    let { promise, resolve } = Promise.withResolvers();
    this.#deleteWorkspaceOwnedTabs(windowID);

-    // mark item as changed for sync
-    this.#markWorkspaceChanged(windowID);
-
    let workspacesData = this.getWorkspaces();
    // Remove the workspace from the cache
    workspacesData = workspacesData.filter(
@@ -1442,11 +1389,6 @@ class nsZenWorkspaces {
      return;
    }
    const workspaces = this.getWorkspaces();
-    // Track previous positions so we only notify observers for workspaces whose
-    // position changed during the reorder.
-    const previousPositions = new Map(
-      workspaces.map((workspace, index) => [workspace.uuid, index])
-    );

    const workspace = workspaces.find(w => w.uuid === id);
    if (!workspace) {
@@ -1475,15 +1417,6 @@ class nsZenWorkspaces {
    // Propagate the changes if the order has changed
    if (currentIndex !== newPosition) {
      this._workspaceCache = workspaces;
-
-      for (const [i, ws] of workspaces.entries()) {
-        if (previousPositions.get(ws.uuid) === i) {
-          continue;
-        }
-        // mark item as changed for sync
-        this.#markWorkspaceChanged(ws.uuid);
-      }
-
      this.#propagateWorkspaceData(workspaces);
    }
  }
@@ -1790,6 +1723,15 @@ class nsZenWorkspaces {
  }

  makeSureEmptyTabIsFirst() {
+    if (
+      gZenUIManager.testingEnabled &&
+      this._emptyTab &&
+      (this._emptyTab.closing || !this._emptyTab.isConnected)
+    ) {
+      this._emptyTab = gBrowser.tabs.find(
+        tab => tab.hasAttribute("zen-empty-tab") && !tab.closing
+      );
+    }
    const emptyTab = this._emptyTab;
    if (emptyTab) {
      emptyTab.setAttribute("zen-workspace-id", this.activeWorkspace);
@@ -3320,8 +3262,10 @@ class nsZenWorkspaces {
      return width;
    }, 0);

-    // Check if the total width exceeds the parent's width
-    if (totalWidth > parent.clientWidth) {
+    // Check if the total width exceeds the parent's width.
+    const parentWidth =
+      window.windowUtils.getBoundsWithoutFlushing(parent).width;
+    if (totalWidth > parentWidth) {
      parent.setAttribute("icons-overflow", "true");
    } else {
      parent.removeAttribute("icons-overflow");
@@ -3329,7 +3273,7 @@ class nsZenWorkspaces {

    // Set the width of each icon to the maximum size they can fit on
    const widthPerButton = Math.max(
-      (parent.clientWidth - separation * (parent.children.length - 1)) /
+      (parentWidth - separation * (parent.children.length - 1)) /
        parent.children.length,
      minButtonSize
    );
--- a/src/zen/spaces/zen-gradient-generator.css
+++ b/src/zen/spaces/zen-gradient-generator.css
@@ -231,6 +231,13 @@
    width: var(--zen-thumb-width);
    cursor: pointer;
    border: none;
+    transform: scale(1);
+    transform-origin: center;
+    transition: transform 0.5s;
+  }
+
+  &:hover::-moz-range-thumb {
+    transform: scale(1.1);
  }

  &::-moz-range-track {
@@ -338,7 +345,7 @@
      display: none;
    }

-    &:hover {
+    &:not([disabled]):hover {
      background: light-dark(rgba(0, 0, 0, 0.1), rgba(255, 255, 255, 0.1));
    }

--- a/src/zen/spaces/zen-workspaces.css
+++ b/src/zen/spaces/zen-workspaces.css
@@ -31,6 +31,7 @@
  & toolbarbutton {
    margin: 0;
    max-width: 28px;
+    border-radius: var(--toolbarbutton-border-radius);
    height: 28px;
    display: flex;
    justify-content: center;
--- a/src/zen/split-view/ZenViewSplitter.mjs
+++ b/src/zen/split-view/ZenViewSplitter.mjs
@@ -230,7 +230,10 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
      }
      this.removeGroup(groupIndex);
      if (changeTab) {
-        gBrowser.selectedTab = remainingTabs[0];
+        const tabToSelect = remainingTabs.find(remaining => remaining !== tab);
+        if (tabToSelect) {
+          gBrowser.selectedTab = tabToSelect;
+        }
        document
          .getElementById("cmd_zenNewEmptySplit")
          .removeAttribute("disabled");
@@ -355,7 +358,9 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
    ) {
      return;
    }
-    const currentView = this._data[this._lastOpenedTab.splitViewValue];
+    const currentView = this._data.find(group =>
+      group.tabs.includes(this._lastOpenedTab)
+    );
    if (currentView?.tabs.length >= this.MAX_TABS) {
      return;
    }
@@ -540,7 +545,9 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
    const panelsWidth = panelsRect.width;
    const panelsHeight = panelsRect.height;
    let numOfTabsToDivide = 2;
-    const currentView = this._data[this._lastOpenedTab.splitViewValue];
+    const currentView = this._data.find(group =>
+      group.tabs.includes(this._lastOpenedTab)
+    );
    if (currentView) {
      numOfTabsToDivide = currentView.tabs.length + 1;
    }
@@ -1103,7 +1110,6 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
   */
  resetTabState(tab, forUnsplit) {
    tab.splitView = false;
-    delete tab.splitViewValue;
    tab.removeAttribute("split-view");
    tab.linkedBrowser.zenModeActive = false;
    const container = tab.linkedBrowser.closest(".browserSidebarContainer");
@@ -1147,6 +1153,8 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
    }
    if (this.currentView === groupIndex) {
      this.deactivateCurrentSplitView();
+    } else if (this.currentView > groupIndex) {
+      this.currentView--;
    }
    for (const tab of this._data[groupIndex].tabs) {
      this.resetTabState(tab, true);
@@ -1638,7 +1646,6 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
  applyGridToTabs(tabs) {
    tabs.forEach(tab => {
      tab.splitView = true;
-      tab.splitViewValue = this.currentView;
      tab.setAttribute("split-view", "true");
      const container = tab.linkedBrowser?.closest(".browserSidebarContainer");
      container.setAttribute("is-zen-split", "true");
@@ -2530,22 +2537,33 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
      this.activateSplitView(data);
      gBrowser.selectedTab = emptyTab;
      setTimeout(() => {
+        const closeToken = {};
+        const controller = new AbortController();
+        const cleanup = (onSwitch = false, groupIndex = null) => {
+          if (groupIndex === null) {
+            groupIndex = this._data.findIndex(group =>
+              group.tabs.includes(emptyTab)
+            );
+          }
+          this.removeTabFromGroup(emptyTab, groupIndex, {
+            changeTab: !onSwitch,
+            forUnsplit: true,
+          });
+          const command = document.getElementById("cmd_zenNewEmptySplit");
+          command.removeAttribute("disabled");
+        };
        window.addEventListener(
          "ZenURLBarClosed",
          event => {
+            if (!gZenUIManager.matchesCloseToken(closeToken, event)) {
+              return;
+            }
+            controller.abort();
            const { onElementPicked, onSwitch } = event.detail;
            const groupIndex = this._data.findIndex(group =>
              group.tabs.includes(emptyTab)
            );
            const newSelectedTab = gBrowser.selectedTab;
-            const cleanup = () => {
-              this.removeTabFromGroup(emptyTab, groupIndex, {
-                changeTab: !onSwitch,
-                forUnsplit: true,
-              });
-              const command = document.getElementById("cmd_zenNewEmptySplit");
-              command.removeAttribute("disabled");
-            };
            if (onElementPicked) {
              if (
                newSelectedTab === emptyTab ||
@@ -2553,7 +2571,7 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
                selectedTab.getAttribute("zen-workspace-id") !==
                  newSelectedTab.getAttribute("zen-workspace-id")
              ) {
-                cleanup();
+                cleanup(onSwitch, groupIndex);
                return;
              }
              this.removeTabFromGroup(emptyTab, groupIndex, {
@@ -2569,12 +2587,17 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
                topOrLeft ? 0 : 1
              );
            } else {
-              cleanup();
+              cleanup(onSwitch, groupIndex);
            }
          },
-          { once: true }
+          { signal: controller.signal }
        );
-        gZenUIManager.handleNewTab(false, false, "tab", true);
+        if (
+          !gZenUIManager.handleNewTab(false, false, "tab", true, closeToken)
+        ) {
+          controller.abort();
+          cleanup();
+        }
      });
    });
  }
--- a/src/zen/sync/ZenSpacesSync.sys.mjs
+++ b/src/zen/sync/ZenSpacesSync.sys.mjs
@@ -0,0 +1,182 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import {
+  Store,
+  SyncEngine,
+  Tracker,
+} from "resource://services-sync/engines.sys.mjs";
+import { CryptoWrapper } from "resource://services-sync/record.sys.mjs";
+import { SCORE_INCREMENT_XLARGE } from "resource://services-sync/constants.sys.mjs";
+import {
+  SIDEBAR_COLLECTED_TOPIC,
+  syncLog,
+  ZenSpacesSyncModel,
+} from "resource:///modules/zen/ZenSpacesSyncModel.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  ZenSpacesSyncApplier: "resource:///modules/zen/ZenSpacesSyncApplier.sys.mjs",
+});
+
+const TRACKED_TOPICS = [
+  SIDEBAR_COLLECTED_TOPIC,
+  "contextual-identity-created",
+  "contextual-identity-updated",
+  "contextual-identity-deleted",
+];
+
+export class ZenSpacesSyncRecord extends CryptoWrapper {
+  _logName = "Sync.Record.ZenSpaces";
+}
+
+ZenSpacesSyncRecord.prototype.type = "spaces";
+
+/**
+ * Store for the Spaces engine. Outgoing records are pure projections of
+ * the session-store sidebar data; incoming batches are handed to the
+ * applier, which reconciles them into the live browser.
+ */
+class ZenSpacesSyncStore extends Store {
+  async getAllIDs() {
+    return ZenSpacesSyncModel.getAllRecordIds();
+  }
+
+  async itemExists(id) {
+    return ZenSpacesSyncModel.itemExists(id);
+  }
+
+  async createRecord(id, collection) {
+    const record = new ZenSpacesSyncRecord(collection, id);
+    const projected = ZenSpacesSyncModel.projectRecord(id);
+    if (!projected) {
+      record.deleted = true;
+      return record;
+    }
+    record.cleartext = { id, kind: projected.kind, data: projected.data };
+    return record;
+  }
+
+  async applyIncomingBatch(records, countTelemetry) {
+    const failed = await lazy.ZenSpacesSyncApplier.applyBatch(records);
+    for (const id of failed) {
+      countTelemetry?.addIncomingFailedReason(`failed to apply ${id}`);
+    }
+    return failed;
+  }
+
+  async wipe() {
+    // Never delete user data on an engine wipe.
+  }
+
+  async changeItemID() {}
+}
+
+/**
+ * Tracker for the Spaces engine. There is no per-event bookkeeping: every
+ * time fresh sidebar data is collected (or a container changes), the model
+ * diffs the current projections against the last-uploaded snapshot; the
+ * score is only bumped when something actually differs.
+ */
+class ZenSpacesSyncTracker extends Tracker {
+  _ignoreAll = false;
+
+  get ignoreAll() {
+    return this._ignoreAll;
+  }
+
+  set ignoreAll(value) {
+    this._ignoreAll = value;
+  }
+
+  onStart() {
+    for (const topic of TRACKED_TOPICS) {
+      Services.obs.addObserver(this, topic);
+    }
+  }
+
+  onStop() {
+    for (const topic of TRACKED_TOPICS) {
+      Services.obs.removeObserver(this, topic);
+    }
+  }
+
+  observe(subject, topic) {
+    if (this.ignoreAll) {
+      return;
+    }
+    if (topic !== SIDEBAR_COLLECTED_TOPIC) {
+      ZenSpacesSyncModel.invalidate();
+    }
+    try {
+      if (ZenSpacesSyncModel.hasPendingChanges()) {
+        syncLog(`tracker: pending changes after ${topic}, requesting sync`);
+        this.score += SCORE_INCREMENT_XLARGE;
+      }
+    } catch (e) {
+      console.error("ZenSpacesSync: change detection failed:", e);
+    }
+  }
+}
+
+export class ZenSpacesSyncEngine extends SyncEngine {
+  constructor(service) {
+    super("Spaces", service);
+  }
+
+  get _storeObj() {
+    return ZenSpacesSyncStore;
+  }
+
+  get _trackerObj() {
+    return ZenSpacesSyncTracker;
+  }
+
+  get _recordObj() {
+    return ZenSpacesSyncRecord;
+  }
+
+  get version() {
+    return 1;
+  }
+
+  get syncPriority() {
+    return 8;
+  }
+
+  get allowSkippedRecord() {
+    // A record that persistently fails to upload is skipped; the snapshot
+    // diff retries it on every following sync anyway.
+    return true;
+  }
+
+  async getChangedIDs() {
+    return ZenSpacesSyncModel.computeChangedIDs();
+  }
+
+  async _reconcile(item) {
+    // Incoming records always apply, and any local divergence re-uploads afterwards
+    // (see ZenSpacesSyncModel.noteApplied). The base reconciliation would
+    // instead drop incoming changes whenever the id is also in the local
+    // changed set, because the snapshot diff stamps its changes with "now"
+    // and the local side would always win the age comparison.
+    //
+    // An id we accept must also leave the outgoing set. Projections only
+    // reflect the applied state after the delayed session collection, so
+    // uploading the id later in this same sync would overwrite the record
+    // we just accepted with the stale pre-apply state (and the other
+    // device would then apply that, endlessly trading states back and
+    // forth). Divergence that survives the collection re-uploads on a
+    // later sync through the snapshot diff.
+    this._modified.delete(item.id);
+    return true;
+  }
+
+  async trackRemainingChanges() {}
+
+  async _onRecordsWritten(succeeded) {
+    ZenSpacesSyncModel.markUploaded(succeeded);
+  }
+}
--- a/src/zen/sync/ZenSpacesSyncApplier.sys.mjs
+++ b/src/zen/sync/ZenSpacesSyncApplier.sys.mjs
@@ -0,0 +1,916 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import {
+  canonicalJSON,
+  LAYOUT_RECORD_ID,
+  RECORD_KINDS,
+  syncableIconUrl,
+  syncLog,
+  ZenSpacesSyncModel,
+} from "resource:///modules/zen/ZenSpacesSyncModel.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  SessionSaver: "resource:///modules/sessionstore/SessionSaver.sys.mjs",
+  E10SUtils: "resource://gre/modules/E10SUtils.sys.mjs",
+  TabStateCache: "resource:///modules/sessionstore/TabStateCache.sys.mjs",
+  ZenWindowSync: "resource:///modules/zen/ZenWindowSync.sys.mjs",
+  ZenLiveFoldersManager:
+    "resource:///modules/zen/ZenLiveFoldersManager.sys.mjs",
+  ContextualIdentityService:
+    "moz-src:///toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs",
+});
+
+const FIRST_SYNC_ANIMATION_PREF = "zen.spaces-sync.first-sync-animation-shown";
+
+/**
+ * Applies batches of incoming Spaces records to the local browser.
+ */
+class nsZenSpacesSyncApplier {
+  #itemIn(win, id) {
+    return id ? win.document.getElementById(id) : null;
+  }
+
+  /**
+   * Maps a record's container guid to the local userContextId. A guid with
+   * no local mapping (its container record hasn't applied here yet) throws,
+   * failing the record so it redelivers once the container exists .
+   *
+   * @param {?string} containerGuid
+   * @returns {number}
+   */
+  #resolveContainerId(containerGuid) {
+    if (!containerGuid) {
+      return 0;
+    }
+    const mapped = ZenSpacesSyncModel.contextIdForGuid(containerGuid);
+    if (mapped === null) {
+      throw new Error(`unknown container guid ${containerGuid}`);
+    }
+    return mapped;
+  }
+
+  /**
+   * @param {Array} records - decrypted incoming records.
+   * @returns {Array<string>} ids of records that failed to apply.
+   */
+  async applyBatch(records) {
+    const incoming = {
+      containers: [],
+      spaces: [],
+      tabs: [],
+      folders: [],
+      splits: [],
+      layout: null,
+      deleted: [],
+    };
+    const handled = new Set();
+
+    for (const record of records) {
+      if (typeof record.id !== "string" || !record.id) {
+        continue;
+      }
+      if (record.deleted) {
+        if (record.id !== LAYOUT_RECORD_ID) {
+          incoming.deleted.push({ key: record.id, record });
+        }
+        handled.add(record);
+        continue;
+      }
+      const data = record.cleartext?.data;
+      if (!data) {
+        continue;
+      }
+      const entry = { key: record.id, data, record };
+      switch (record.cleartext.kind) {
+        case RECORD_KINDS.CONTAINER:
+          incoming.containers.push(entry);
+          break;
+        case RECORD_KINDS.SPACE:
+          incoming.spaces.push(entry);
+          break;
+        case RECORD_KINDS.TAB:
+          incoming.tabs.push(entry);
+          break;
+        case RECORD_KINDS.FOLDER:
+          incoming.folders.push(entry);
+          break;
+        case RECORD_KINDS.SPLIT:
+          incoming.splits.push(entry);
+          break;
+        case RECORD_KINDS.LAYOUT:
+          incoming.layout = entry;
+          break;
+        default:
+          // Unknown kind (newer client): leave untouched and unacknowledged.
+          continue;
+      }
+      handled.add(record);
+    }
+
+    syncLog(
+      `incoming batch: ${incoming.containers.length} containers, ` +
+        `${incoming.spaces.length} spaces, ${incoming.tabs.length} tabs, ` +
+        `${incoming.folders.length} folders, ${incoming.splits.length} splits, ` +
+        `layout=${!!incoming.layout}, ${incoming.deleted.length} tombstones`
+    );
+
+    const failed = new Set();
+    const fail = (record, e) => {
+      failed.add(record.id);
+      console.error(`ZenSpacesSync: failed to apply ${record.id}:`, e);
+    };
+
+    const deletions = this.#applyContainers(incoming, fail);
+
+    const win = lazy.ZenWindowSync.firstSyncedWindow;
+    if (!win) {
+      // Report the records as failed so the engine redelivers the batch on a later sync.
+      const noWindow = new Error("no synced window to apply into");
+      for (const entry of [
+        ...incoming.spaces,
+        ...incoming.folders,
+        ...incoming.tabs,
+        ...incoming.splits,
+        ...(incoming.layout ? [incoming.layout] : []),
+        ...deletions,
+      ]) {
+        fail(entry.record, noWindow);
+      }
+    } else {
+      await win.gZenWorkspaces.promiseInitialized;
+      this.#maybePlayFirstSyncAnimation(win);
+      const removals = this.#routeTombstones(win, deletions);
+      this.#deleteTabs(win, removals.tabs, fail);
+      this.#deleteSplits(win, removals.splits, fail);
+      await this.#applySpaces(win, incoming.spaces, fail);
+      await this.#applyFolders(win, incoming.folders, fail);
+      this.#applyTabs(win, incoming.tabs, fail);
+      this.#applySplits(win, incoming.splits, fail);
+      await this.#deleteFolders(win, removals.folders, fail);
+      await this.#deleteSpaces(win, removals.spaces, fail);
+      this.#applyOrdering(win, incoming, fail);
+      // Collect the session soon so the stored sidebar (and with it the
+      // sync projections) reflects the applied state instead of re-uploading
+      // the pre-apply one.
+      lazy.SessionSaver.runDelayed();
+    }
+
+    ZenSpacesSyncModel.invalidate();
+    for (const record of records) {
+      if (!handled.has(record) || failed.has(record.id)) {
+        continue;
+      }
+      ZenSpacesSyncModel.noteApplied(
+        record.id,
+        record.deleted ? null : record.cleartext
+      );
+    }
+    return [...failed];
+  }
+
+  /**
+   * Plays the update sweep animation over the window the first time
+   * incoming sync data lands on this profile.
+   *
+   * @param {Window} win
+   */
+  #maybePlayFirstSyncAnimation(win) {
+    if (Services.prefs.getBoolPref(FIRST_SYNC_ANIMATION_PREF, false)) {
+      return;
+    }
+    Services.prefs.setBoolPref(FIRST_SYNC_ANIMATION_PREF, true);
+    win.gZenStartup.playWindowSweepAnimation();
+  }
+
+  /**
+   * Tombstones have no payload. Whatever local thing owns the id decides
+   * what kind of deletion this is. Ids with no local counterpart need no
+   * work at all.
+   *
+   * @param {Window} win
+   * @param {Array<{key: string, record: object}>} deletions
+   */
+  #routeTombstones(win, deletions) {
+    const routed = { tabs: [], folders: [], splits: [], spaces: [] };
+    const spaces = win.gZenWorkspaces.getWorkspaces();
+    for (const entry of deletions) {
+      const el = this.#itemIn(win, entry.key);
+      if (win.gBrowser.isTab(el)) {
+        routed.tabs.push(entry);
+      } else if (el?.isZenFolder) {
+        routed.folders.push(entry);
+      } else if (el?.hasAttribute?.("split-view-group")) {
+        routed.splits.push(entry);
+      } else if (spaces.some(s => s.uuid === entry.key)) {
+        routed.spaces.push(entry);
+      }
+    }
+    if (deletions.length) {
+      const matched = new Set([
+        ...routed.tabs,
+        ...routed.folders,
+        ...routed.splits,
+        ...routed.spaces,
+      ]);
+      syncLog("tombstones routed:", {
+        tabs: routed.tabs.map(e => e.key),
+        folders: routed.folders.map(e => e.key),
+        splits: routed.splits.map(e => e.key),
+        spaces: routed.spaces.map(e => e.key),
+        unmatched: deletions.filter(e => !matched.has(e)).map(e => e.key),
+      });
+    }
+    return routed;
+  }
+
+  /* Mark: containers */
+
+  #applyContainers(incoming, fail) {
+    for (const { key: guid, data, record } of incoming.containers) {
+      try {
+        if (!data.name) {
+          continue;
+        }
+        const mapped = ZenSpacesSyncModel.contextIdForGuid(guid);
+        const existing =
+          mapped !== null
+            ? lazy.ContextualIdentityService.getPublicIdentityFromId(mapped)
+            : null;
+        if (existing) {
+          lazy.ContextualIdentityService.update(
+            mapped,
+            data.name,
+            data.icon,
+            data.color
+          );
+        } else {
+          const identity = lazy.ContextualIdentityService.create(
+            data.name,
+            data.icon,
+            data.color
+          );
+          ZenSpacesSyncModel.registerContainerGuid(
+            guid,
+            identity.userContextId
+          );
+        }
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+
+    const rest = [];
+    for (const entry of incoming.deleted) {
+      const mapped = ZenSpacesSyncModel.contextIdForGuid(entry.key);
+      if (mapped === null) {
+        rest.push(entry);
+        continue;
+      }
+      try {
+        if (lazy.ContextualIdentityService.getPublicIdentityFromId(mapped)) {
+          lazy.ContextualIdentityService.remove(mapped);
+        }
+        ZenSpacesSyncModel.forgetContainerGuid(entry.key);
+      } catch (e) {
+        fail(entry.record, e);
+      }
+    }
+    return rest;
+  }
+
+  /* Mark: spaces */
+
+  async #applySpaces(win, spaces, fail) {
+    if (!spaces.length) {
+      return;
+    }
+    const list = win.gZenWorkspaces.getWorkspaces();
+    let changed = false;
+    const repaint = [];
+    for (const { data, record } of spaces) {
+      try {
+        if (!data.uuid) {
+          continue;
+        }
+        const fields = {
+          uuid: data.uuid,
+          name: data.name ?? "",
+          icon: data.icon ?? undefined,
+          theme: data.theme ?? null,
+          containerTabId: this.#resolveContainerId(data.containerGuid),
+        };
+        // A space record re-syncs whenever its child ordering changes, so
+        // only propagate (and especially repaint) when its own fields did.
+        const index = list.findIndex(s => s.uuid === data.uuid);
+        const current = index === -1 ? null : list[index];
+        const visualChanged =
+          !current ||
+          (current.name ?? "") !== fields.name ||
+          (current.icon ?? null) !== (fields.icon ?? null) ||
+          canonicalJSON(current.theme ?? null) !==
+            canonicalJSON(fields.theme ?? null);
+        const containerChanged =
+          !current || (current.containerTabId ?? 0) !== fields.containerTabId;
+        if (containerChanged) {
+          syncLog(
+            `space ${data.uuid} containerTabId ` +
+              `${current?.containerTabId ?? 0} -> ${fields.containerTabId} ` +
+              `(guid ${data.containerGuid ?? "none"})`
+          );
+        }
+        if (!current) {
+          list.push(fields);
+          changed = true;
+        } else if (visualChanged || containerChanged) {
+          list[index] = { ...current, ...fields };
+          changed = true;
+        }
+        if (visualChanged) {
+          repaint.push(data.uuid);
+        }
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+    if (changed) {
+      await win.gZenWorkspaces.propagateWorkspaces(list);
+      win.gZenWindowSync.propagateWorkspacesToAllWindows(list);
+      for (const uuid of repaint) {
+        const updated = list.find(s => s.uuid === uuid);
+        if (updated) {
+          win.gZenThemePicker.onWorkspaceChange(updated);
+        }
+      }
+    }
+  }
+
+  async #deleteSpaces(win, removals, fail) {
+    for (const { key: uuid, record } of removals) {
+      try {
+        const spaces = win.gZenWorkspaces.getWorkspaces();
+        if (!spaces.some(s => s.uuid === uuid)) {
+          continue;
+        }
+        if (spaces.length <= 1) {
+          // Never delete the last space; the local copy revives it remotely.
+          continue;
+        }
+        if (!(await this.#confirmRemoteSpaceDelete(win, uuid))) {
+          continue;
+        }
+        await win.gZenWorkspaces.removeWorkspace(uuid);
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+  }
+
+  /**
+   * @param {Window} win
+   * @param {string} uuid
+   * @returns {Promise<boolean>} Whether the user confirmed the deletion.
+   */
+  async #confirmRemoteSpaceDelete(win, uuid) {
+    const name = win.gZenWorkspaces.getWorkspaceFromId(uuid)?.name || uuid;
+    const [title, body] = await win.document.l10n.formatValues([
+      { id: "zen-workspaces-remote-delete-title" },
+      { id: "zen-workspaces-remote-delete-body", args: { name } },
+    ]);
+    const result = await Services.prompt.asyncConfirmEx(
+      win.browsingContext,
+      Services.prompt.MODAL_TYPE_WINDOW,
+      title,
+      body,
+      Services.prompt.STD_YES_NO_BUTTONS,
+      null,
+      null,
+      null,
+      null,
+      false
+    );
+    return result.get("buttonNumClicked") === 0;
+  }
+
+  /* Mark: folders */
+
+  async #applyFolders(win, folders, fail) {
+    // Parents before children so nesting targets exist.
+    const depths = new Map(folders.map(f => [f.key, f.data.parentFolderId]));
+    const depthOf = key => {
+      let depth = 0;
+      let parent = depths.get(key);
+      while (parent && depths.has(parent) && depth < 10) {
+        depth++;
+        parent = depths.get(parent);
+      }
+      return depth;
+    };
+    const ordered = [...folders].sort(
+      (a, b) => depthOf(a.key) - depthOf(b.key)
+    );
+
+    for (const { key: folderId, data, record } of ordered) {
+      try {
+        let folder = this.#itemIn(win, folderId);
+        if (!folder?.isZenFolder) {
+          folder = win.gZenFolders.createFolder([], {
+            id: folderId,
+            label: data.name || "Folder",
+            workspaceId:
+              data.workspaceUuid || win.gZenWorkspaces.activeWorkspace,
+            isLiveFolder: !!data.live,
+          });
+        } else if (data.name && folder.label !== data.name) {
+          folder.label = data.name;
+        }
+
+        if (data.live && !folder.isLiveFolder) {
+          // The folder synced before its provider config was available and
+          // materialized as a plain folder; upgrade it so this profile
+          // projects the config too instead of clobbering it with live: null.
+          folder.isLiveFolder = true;
+        }
+
+        if ((folder.iconURL || null) !== (data.icon || null)) {
+          win.gZenFolders.setFolderUserIcon(folder, data.icon || null);
+          // Window sync picks this up and mirrors the icon everywhere else.
+          folder.dispatchEvent(
+            new win.CustomEvent("TabGroupUpdate", { bubbles: true })
+          );
+        }
+
+        const desiredParent = data.parentFolderId
+          ? this.#itemIn(win, data.parentFolderId)
+          : null;
+        const currentParent = folder.group;
+        if ((currentParent?.id || null) !== (data.parentFolderId || null)) {
+          if (desiredParent?.isZenFolder) {
+            win.gBrowser.zenHandleTabMove(folder, () => {
+              if (desiredParent.tabs.length) {
+                desiredParent.tabs[0].after(folder);
+              } else {
+                desiredParent.appendChild(folder);
+              }
+            });
+          } else if (!data.parentFolderId && currentParent?.isZenFolder) {
+            const ws = data.workspaceUuid || win.gZenWorkspaces.activeWorkspace;
+            const container =
+              win.gZenWorkspaces.workspaceElement(ws)?.pinnedTabsContainer;
+            if (container) {
+              win.gBrowser.zenHandleTabMove(folder, () => {
+                container.insertBefore(
+                  folder,
+                  container.querySelector(".pinned-tabs-container-separator")
+                );
+              });
+            }
+          }
+        }
+        if (
+          data.workspaceUuid &&
+          folder.getAttribute("zen-workspace-id") !== data.workspaceUuid
+        ) {
+          if (!folder.group) {
+            win.gZenFolders.changeFolderToSpace(folder, data.workspaceUuid);
+          } else {
+            folder.setAttribute("zen-workspace-id", data.workspaceUuid);
+          }
+        }
+        if (data.live) {
+          await lazy.ZenLiveFoldersManager.adoptSyncedFolder(
+            folderId,
+            data.live
+          );
+        }
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+  }
+
+  async #deleteFolders(win, removals, fail) {
+    for (const { key: folderId, record } of removals) {
+      try {
+        const folder = this.#itemIn(win, folderId);
+        if (!folder?.isZenFolder) {
+          continue;
+        }
+        // Members without their own tombstone survive: unpack, then delete
+        // the (now empty) folder.
+        await folder.unpackTabs();
+        await folder.delete();
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+  }
+
+  /* Mark: tabs */
+
+  #applyTabs(win, tabs, fail) {
+    for (const { key: tabId, data, record } of tabs) {
+      try {
+        if (!data.url || data.url === "about:blank") {
+          continue;
+        }
+        const existing = this.#itemIn(win, tabId);
+        if (win.gBrowser.isTab(existing)) {
+          this.#updateTab(win, existing, data);
+        } else {
+          this.#createTab(win, tabId, data);
+        }
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+  }
+
+  #createTab(win, tabId, data) {
+    const userContextId = this.#resolveContainerId(data.containerGuid);
+    syncLog(
+      `creating tab ${tabId} ` +
+        `(essential=${!!data.essential}, container=${userContextId})`,
+      data.url
+    );
+    const tab = win.gBrowser.addTrustedTab(data.url, {
+      createLazyBrowser: true,
+      inBackground: true,
+      skipAnimation: true,
+      skipBackgroundNotify: true,
+      lazyTabTitle: data.title || undefined,
+      userContextId,
+      skipRoute: true,
+    });
+    // Setting the sync id before the queued TabOpen handler runs makes
+    // window sync treat this tab as already replicated.
+    tab.id = tabId;
+    tab._zenContentsVisible = true;
+    this.#updateTabIdentity(win, tab, data);
+    if (data.essential) {
+      win.gZenPinnedTabManager.addToEssentials(tab, { replicating: true });
+    } else {
+      if (data.workspaceUuid) {
+        tab.setAttribute("zen-workspace-id", data.workspaceUuid);
+      }
+      win.gBrowser.pinTab(tab);
+      if (data.workspaceUuid) {
+        win.gZenWorkspaces.moveTabToWorkspace(tab, data.workspaceUuid);
+      }
+      const folder = data.folderId && this.#itemIn(win, data.folderId);
+      if (folder?.isZenFolder) {
+        folder.addTabs([tab]);
+      }
+    }
+    lazy.ZenWindowSync.on_TabOpen({ target: tab }, { ignoreExistingId: true });
+  }
+
+  /**
+   * Reconciles the tab's synced identity: pinned initial state, static
+   * label/icon, the live icon and the default-container marker.
+   *
+   * @param {Window} win
+   * @param {MozTabbrowserTab} tab
+   * @param {object} data
+   */
+  #updateTabIdentity(win, tab, data) {
+    const icon = syncableIconUrl(data.icon);
+    const initial = tab._zenPinnedInitialState;
+    const identityChanged =
+      initial?.entry?.url !== data.url ||
+      (initial?.entry?.title || "") !== (data.title || "");
+    if (identityChanged || syncableIconUrl(initial?.image || "") !== icon) {
+      lazy.ZenWindowSync.setPinnedInitialState(
+        tab,
+        { url: data.url, title: data.title || "" },
+        icon || undefined
+      );
+    }
+    if (identityChanged && !tab.linkedPanel) {
+      // An unloaded tab has no live state to lose: retarget its lazy session
+      // state so the next activation loads the new canonical url directly
+      // instead of whatever the tab was created with.
+      this.#retargetUnloadedTab(win, tab, data, initial?.entry?.url);
+    }
+
+    const staticLabel =
+      typeof data.staticLabel === "string" ? data.staticLabel : null;
+    const localLabel =
+      typeof tab.zenStaticLabel === "string" ? tab.zenStaticLabel : null;
+    if (staticLabel !== localLabel) {
+      tab.zenStaticLabel = staticLabel ?? undefined;
+      if (staticLabel) {
+        tab._zenChangeLabelFlag = true;
+        try {
+          win.gBrowser._setTabLabel(tab, staticLabel);
+        } finally {
+          delete tab._zenChangeLabelFlag;
+        }
+      }
+    }
+    tab.zenStaticIcon = data.hasStaticIcon && icon ? icon : undefined;
+    const iconDiffers =
+      icon && syncableIconUrl(tab.getAttribute("image")) !== icon;
+    if (iconDiffers && (data.hasStaticIcon || !tab.linkedPanel)) {
+      try {
+        syncLog(
+          `setting synced${data.hasStaticIcon ? " static" : ""} ` +
+            `icon on tab ${tab.id}`
+        );
+        win.gBrowser.setIcon(tab, icon);
+        lazy.TabStateCache.update(tab.linkedBrowser.permanentKey, {
+          image: null,
+        });
+      } catch (e) {
+        console.error("ZenSpacesSync: failed to set tab icon", e);
+      }
+    }
+    if (data.defaultContainer) {
+      tab.setAttribute("zenDefaultUserContextId", "true");
+    } else {
+      tab.removeAttribute("zenDefaultUserContextId");
+    }
+  }
+
+  /**
+   * Points an unloaded tab's session state at the record's canonical url,
+   * mirroring ZenPinnedTabManager's reset-to-stored-state shape.
+   *
+   * @param {Window} win
+   * @param {MozTabbrowserTab} tab
+   * @param {object} data
+   * @param {?string} previousPinUrl - The pin url before this record applied.
+   */
+  #retargetUnloadedTab(win, tab, data, previousPinUrl) {
+    try {
+      const state = JSON.parse(win.SessionStore.getTabState(tab));
+      const entries = state.entries || [];
+      let currentUrl = null;
+      if (entries.length) {
+        const index = Math.min(
+          Math.max((state.index || entries.length) - 1, 0),
+          entries.length - 1
+        );
+        currentUrl = entries[index]?.url || null;
+      }
+      if (
+        currentUrl === data.url ||
+        (currentUrl && previousPinUrl && currentUrl !== previousPinUrl)
+      ) {
+        return;
+      }
+      state.entries = [
+        {
+          url: data.url,
+          title: data.title || "",
+          triggeringPrincipal_base64: lazy.E10SUtils.serializePrincipal(
+            Services.scriptSecurityManager.createContentPrincipal(
+              Services.io.newURI(data.url),
+              {}
+            )
+          ),
+        },
+      ];
+      state.index = 1;
+      state.image = syncableIconUrl(data.icon) || undefined;
+      delete state.scroll;
+      win.SessionStore.setTabState(tab, state);
+    } catch (e) {
+      console.error("ZenSpacesSync: failed to retarget unloaded tab", e);
+    }
+  }
+
+  /**
+   * Puts a tab or split group under the folder the record names, or back at
+   * top level when it names none.
+   *
+   * @param {Window} win
+   * @param {MozTabbrowserTab|MozTabbrowserTabGroup} item
+   * @param {?string} folderId
+   */
+  #applyFolderMembership(win, item, folderId) {
+    const currentFolder = item.group?.isZenFolder ? item.group.id : null;
+    const wantFolder = folderId || null;
+    if (currentFolder === wantFolder) {
+      return;
+    }
+    const target = wantFolder && this.#itemIn(win, wantFolder);
+    if (target?.isZenFolder) {
+      target.addTabs([item]);
+    } else if (!wantFolder && currentFolder) {
+      // ungroupTab pops a single nesting level. An item inside a subfolder
+      // lands inside the parent folder, so keep going until it is actually
+      // top-level.
+      while (win.gBrowser.isTabGroup(item.group) && item.group.isZenFolder) {
+        win.gBrowser.ungroupTab(item);
+      }
+    }
+  }
+
+  #updateTab(win, tab, data) {
+    this.#updateTabIdentity(win, tab, data);
+
+    const isEssential = tab.hasAttribute("zen-essential");
+    if (data.essential && !isEssential) {
+      syncLog(`incoming record promotes tab ${tab.id} to essential`);
+      win.gZenPinnedTabManager.addToEssentials(tab, { replicating: true });
+      return;
+    }
+    if (!data.essential && isEssential) {
+      console.warn(
+        `ZenSpacesSync: incoming record demotes essential tab ${tab.id}`
+      );
+      win.gZenPinnedTabManager.removeEssentials(tab, /* unpin */ false);
+    }
+    if (data.essential) {
+      return;
+    }
+
+    const inSplit = tab.group?.hasAttribute("split-view-group");
+    if (inSplit) {
+      // The split record governs placement of its members.
+      return;
+    }
+    this.#applyFolderMembership(win, tab, data.folderId);
+    if (
+      !data.folderId &&
+      data.workspaceUuid &&
+      tab.getAttribute("zen-workspace-id") !== data.workspaceUuid
+    ) {
+      win.gZenWorkspaces.moveTabToWorkspace(tab, data.workspaceUuid);
+    }
+  }
+
+  #removeTab(win, tab) {
+    if (tab.splitView) {
+      win.gZenViewSplitter.removeTabFromGroup(tab, undefined, {
+        forUnsplit: true,
+        changeTab: false,
+      });
+    }
+    win.gBrowser.removeTab(tab, { animate: true });
+  }
+
+  #deleteTabs(win, removals, fail) {
+    for (const { key: tabId, record } of removals) {
+      try {
+        const tab = this.#itemIn(win, tabId);
+        if (win.gBrowser.isTab(tab)) {
+          if (tab.hasAttribute("zen-essential")) {
+            console.warn(
+              `ZenSpacesSync: incoming tombstone removes essential tab ${tabId}`,
+              tab.linkedBrowser?.currentURI?.spec ?? ""
+            );
+          } else {
+            syncLog(`incoming tombstone removes tab ${tabId}`);
+          }
+          this.#removeTab(win, tab);
+        }
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+  }
+
+  /* Mark: splits */
+
+  #applySplits(win, splits, fail) {
+    for (const { key: splitId, data, record } of splits) {
+      try {
+        const members = (data.tabs || [])
+          .map(id => this.#itemIn(win, id))
+          .filter(tab => win.gBrowser.isTab(tab));
+        const existing = this.#itemIn(win, splitId);
+        const hasGroup = existing?.hasAttribute?.("split-view-group");
+        if (hasGroup) {
+          const wanted = new Set(data.tabs || []);
+          for (const tab of [...existing.tabs]) {
+            if (tab.id && !wanted.has(tab.id)) {
+              win.gZenViewSplitter.removeTabFromGroup(tab, undefined, {
+                changeTab: false,
+              });
+            }
+          }
+        }
+        if (members.length >= 2) {
+          win.gZenViewSplitter.splitTabs(members, data.gridType, -1, {
+            groupFetchId: splitId,
+          });
+        }
+        const group = this.#itemIn(win, splitId);
+        if (group?.hasAttribute?.("split-view-group")) {
+          this.#applyFolderMembership(win, group, data.folderId);
+        }
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+  }
+
+  #deleteSplits(win, removals, fail) {
+    for (const { key: splitId, record } of removals) {
+      try {
+        const index = win.gZenViewSplitter._data.findIndex(
+          group => group.groupId === splitId
+        );
+        if (index >= 0) {
+          win.gZenViewSplitter.removeGroup(index);
+        }
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+  }
+
+  /* Mark: ordering */
+
+  #applyRelativeOrder(win, elements) {
+    let prev = null;
+    for (const el of elements) {
+      if (!el) {
+        continue;
+      }
+      if (
+        prev &&
+        prev.parentNode &&
+        prev.parentNode === el.parentNode &&
+        prev.nextElementSibling !== el
+      ) {
+        win.gBrowser.zenHandleTabMove(el, () => prev.after(el));
+      }
+      prev = el;
+    }
+  }
+
+  /**
+   * Ordering runs in the first synced window only: every move goes through
+   * zenHandleTabMove, whose TabMove events window sync replicates into the
+   * other windows.
+   *
+   * @param {Window} win
+   * @param {object} incoming
+   * @param {Function} fail
+   */
+  #applyOrdering(win, incoming, fail) {
+    for (const { key, data, record } of [
+      ...incoming.spaces,
+      ...incoming.folders,
+    ]) {
+      try {
+        if (Array.isArray(data.children) && data.children.length) {
+          // A folder's empty-tab placeholder anchors its first child: without
+          // it, relative ordering could never move anything to the start.
+          const folder = data.folderId ? this.#itemIn(win, key) : null;
+          const start = folder?.isZenFolder
+            ? folder.tabs.find(t => t.hasAttribute("zen-empty-tab"))
+            : null;
+          this.#applyRelativeOrder(win, [
+            start ?? null,
+            ...data.children.map(id => this.#itemIn(win, id)),
+          ]);
+        }
+      } catch (e) {
+        fail(record, e);
+      }
+    }
+    if (!incoming.layout) {
+      return;
+    }
+    const { data, record } = incoming.layout;
+    try {
+      for (const tabIds of Object.values(data.essentials || {})) {
+        if (Array.isArray(tabIds) && tabIds.length > 1) {
+          this.#applyRelativeOrder(
+            win,
+            tabIds.map(id => this.#itemIn(win, id))
+          );
+        }
+      }
+      if (Array.isArray(data.spaces) && data.spaces.length > 1) {
+        const current = win.gZenWorkspaces.getWorkspaces();
+        const byUuid = new Map(current.map(s => [s.uuid, s]));
+        const ordered = data.spaces
+          .map(uuid => byUuid.get(uuid))
+          .filter(Boolean);
+        for (const space of current) {
+          if (!data.spaces.includes(space.uuid)) {
+            ordered.push(space);
+          }
+        }
+        const changedOrder = ordered.some(
+          (space, i) => current[i]?.uuid !== space.uuid
+        );
+        if (changedOrder && ordered.length === current.length) {
+          win.gZenWindowSync.propagateWorkspacesToAllWindows(ordered);
+        }
+      }
+    } catch (e) {
+      fail(record, e);
+    }
+  }
+}
+
+export const ZenSpacesSyncApplier = new nsZenSpacesSyncApplier();
--- a/src/zen/sync/ZenSpacesSyncModel.sys.mjs
+++ b/src/zen/sync/ZenSpacesSyncModel.sys.mjs
@@ -0,0 +1,737 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { JSONFile } from "resource://gre/modules/JSONFile.sys.mjs";
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  ZenSessionStore: "resource:///modules/zen/ZenSessionManager.sys.mjs",
+  ZenLiveFoldersManager:
+    "resource:///modules/zen/ZenLiveFoldersManager.sys.mjs",
+  ContextualIdentityService:
+    "moz-src:///toolkit/components/contextualidentity/ContextualIdentityService.sys.mjs",
+});
+
+XPCOMUtils.defineLazyPreferenceGetter(
+  lazy,
+  "syncDebug",
+  "zen.spaces-sync.debug",
+  false
+);
+
+/**
+ * Debug logging for the whole Spaces sync pipeline.
+ *
+ * @param {string} message
+ * @param {...any} args
+ */
+export function syncLog(message, ...args) {
+  if (lazy.syncDebug) {
+    // eslint-disable-next-line no-console
+    console.debug(`ZenSpacesSync: ${message}`, ...args);
+  }
+}
+
+export const SIDEBAR_COLLECTED_TOPIC = "zen-sidebar-data-collected";
+
+export const RECORD_KINDS = Object.freeze({
+  CONTAINER: "container",
+  SPACE: "space",
+  TAB: "tab",
+  FOLDER: "folder",
+  SPLIT: "split",
+  LAYOUT: "layout",
+});
+
+export const LAYOUT_RECORD_ID = "layout";
+
+// Firefox ships four built-in containers with fixed userContextIds. They
+// exist on every device, so they map to well-known guids instead of the
+// per-profile generated ones.
+const BUILTIN_CONTAINER_MAX = 4;
+const BUILTIN_GUID_PREFIX = "builtin-";
+
+const STORE_FILE_NAME = "zen-spaces-sync.json";
+const STORE_VERSION = 1;
+
+// Everything setIcon accepts without a loading principal.
+const LOCAL_ICON_PROTOCOLS = ["data:", "chrome:", "about:", "resource:"];
+
+/**
+ * Normalizes a tab icon for syncing. The image attribute can hold a
+ * moz-remote-image: wrapper around the actual (svg data:) favicon, carrying
+ * a per-process contentParentId that means nothing on another device — sync
+ * the wrapped URL instead. Anything else setIcon would reject as remote is
+ * dropped.
+ *
+ * @param {?string} icon
+ * @returns {string}
+ */
+export function syncableIconUrl(icon) {
+  if (!icon || typeof icon !== "string") {
+    return "";
+  }
+  if (icon.startsWith("moz-remote-image:")) {
+    try {
+      const uri = Services.io.newURI(icon);
+      icon = new URLSearchParams(uri.query).get("url") || "";
+    } catch (e) {
+      return "";
+    }
+  }
+  return LOCAL_ICON_PROTOCOLS.some(protocol => icon.startsWith(protocol))
+    ? icon
+    : "";
+}
+
+function sortedClone(value) {
+  if (Array.isArray(value)) {
+    return value.map(sortedClone);
+  }
+  if (value && typeof value === "object") {
+    const out = {};
+    for (const key of Object.keys(value).sort()) {
+      out[key] = sortedClone(value[key]);
+    }
+    return out;
+  }
+  return value === undefined ? null : value;
+}
+
+/**
+ * Deterministic JSON serialization (recursively sorted keys), so that two
+ * structurally equal payloads always stringify identically.
+ *
+ * @param {object} value
+ */
+export function canonicalJSON(value) {
+  return JSON.stringify(sortedClone(value));
+}
+
+/**
+ * Digest of a record's canonical form. The uploaded-state snapshot only ever
+ * needs equality checks, so it stores these short digests instead of the
+ * full canonical strings, keeping the store file small and cheap to write.
+ *
+ * @param {string} kind
+ * @param {object} data
+ * @returns {string} base64 SHA-256 of the canonical record payload.
+ */
+const textEncoder = new TextEncoder();
+
+export function recordDigest(kind, data) {
+  const hasher = Cc["@mozilla.org/security/hash;1"].createInstance(
+    Ci.nsICryptoHash
+  );
+  hasher.init(Ci.nsICryptoHash.SHA256);
+  const bytes = textEncoder.encode(canonicalJSON({ kind, data }));
+  hasher.update(bytes, bytes.length);
+  return hasher.finish(/* base64 = */ true);
+}
+
+/**
+ * Owns the synced-data model for the Spaces engine.
+ */
+class nsZenSpacesSyncModel {
+  #file = null;
+  #cache = null;
+
+  #data() {
+    if (!this.#file) {
+      this.#file = new JSONFile({
+        path: PathUtils.join(PathUtils.profileDir, STORE_FILE_NAME),
+        dataPostProcessor: data => {
+          if (data.version !== STORE_VERSION) {
+            // Drop the uploaded snapshot so everything re-diffs against
+            // the (also wiped) server, but keep the container identity mappings.
+            data.uploaded = {};
+          }
+          data.version = STORE_VERSION;
+          data.uploaded ||= {};
+          data.containers ||= {};
+          // The container map used to be keyed by guid. It is keyed by
+          // userContextId now so that registering a guid replaces any
+          // previous one for the same container. Flip old stores over
+          // (old values are numeric ids, new values are guid strings).
+          for (const [key, value] of Object.entries(data.containers)) {
+            if (typeof value === "number") {
+              delete data.containers[key];
+              data.containers[value] = key;
+            }
+          }
+          return data;
+        },
+      });
+      this.#file.ensureDataReady();
+    }
+    return this.#file.data;
+  }
+
+  invalidate() {
+    this.#cache = null;
+  }
+
+  /* Mark: container identity */
+
+  guidForContextId(userContextId, { create = false } = {}) {
+    const id = Number(userContextId);
+    if (!Number.isSafeInteger(id) || id <= 0) {
+      return null;
+    }
+    const data = this.#data();
+    if (!lazy.ContextualIdentityService.getPublicIdentityFromId(id)) {
+      // A space or tab still pointing at a container that was deleted.
+      if (id in data.containers) {
+        delete data.containers[id];
+        this.#file.saveSoon();
+      }
+      return null;
+    }
+    if (id <= BUILTIN_CONTAINER_MAX) {
+      return `${BUILTIN_GUID_PREFIX}${id}`;
+    }
+    const existing = data.containers[id];
+    if (existing) {
+      return existing;
+    }
+    if (!create) {
+      return null;
+    }
+    const guid = Services.uuid.generateUUID().toString().slice(1, -1);
+    data.containers[id] = guid;
+    this.#file.saveSoon();
+    return guid;
+  }
+
+  contextIdForGuid(guid) {
+    if (typeof guid !== "string" || !guid) {
+      return null;
+    }
+    const data = this.#data();
+    for (const [id, mapped] of Object.entries(data.containers)) {
+      if (mapped === guid) {
+        const contextId = Number(id);
+        if (lazy.ContextualIdentityService.getPublicIdentityFromId(contextId)) {
+          return contextId;
+        }
+        delete data.containers[id];
+        this.#file.saveSoon();
+        return null;
+      }
+    }
+    if (guid.startsWith(BUILTIN_GUID_PREFIX)) {
+      const id = Number(guid.slice(BUILTIN_GUID_PREFIX.length));
+      return Number.isSafeInteger(id) &&
+        id > 0 &&
+        id <= BUILTIN_CONTAINER_MAX &&
+        lazy.ContextualIdentityService.getPublicIdentityFromId(id)
+        ? id
+        : null;
+    }
+    return null;
+  }
+
+  /**
+   * Adopts an incoming guid as the identity's synced name.
+   *
+   * @param {string} guid
+   * @param {number} userContextId
+   */
+  registerContainerGuid(guid, userContextId) {
+    this.#data().containers[userContextId] = guid;
+    this.#file.saveSoon();
+  }
+
+  forgetContainerGuid(guid) {
+    const data = this.#data();
+    for (const [id, mapped] of Object.entries(data.containers)) {
+      if (mapped === guid) {
+        delete data.containers[id];
+        this.#file.saveSoon();
+        return;
+      }
+    }
+  }
+
+  /* Mark: projections */
+
+  #isSyncableTab(tabData) {
+    return !!(
+      tabData &&
+      tabData.zenSyncId &&
+      (tabData.pinned || tabData.zenEssential) &&
+      !tabData.zenIsEmpty &&
+      !tabData.zenIsGlance &&
+      !tabData.zenLiveFolderItemId
+    );
+  }
+
+  #tabIdentity(tabData) {
+    const initial = tabData._zenPinnedInitialState;
+    let url = initial?.entry?.url;
+    let title = initial?.entry?.title;
+    if (!url || url === "about:blank") {
+      const entries = tabData.entries || [];
+      if (entries.length) {
+        let index = Math.min(
+          Math.max((tabData.index || entries.length) - 1, 0),
+          entries.length - 1
+        );
+        const entry = entries[index] || entries[0];
+        if (entry?.url && entry.url !== "about:blank") {
+          url = entry.url;
+          title ??= entry.title;
+        }
+      }
+    }
+    if (!url || url === "about:blank") {
+      return null;
+    }
+    const icon = syncableIconUrl(
+      (tabData.zenHasStaticIcon
+        ? tabData.image
+        : initial?.image || tabData.image) || ""
+    );
+    return { url, title: title || "", icon };
+  }
+
+  /**
+   * Builds the ordered child id list for one parent (a space's pinned
+   * section or a folder). Tabs and splits are ordered by their position in
+   * the collected tab list; folders are spliced in next to their recorded
+   * previous sibling.
+   *
+   * @param {object} root0
+   * @param {Array<object>} root0.tabs
+   * @param {Array<object>} root0.folders
+   * @param {Set<string>} root0.splitIds
+   * @param {Map<string, ?string>} root0.splitParents
+   * @param {Map<string, ?string>} root0.splitWs
+   * @param {object} root0.scope
+   */
+  #childSequence({ tabs, folders, splitIds, splitParents, splitWs, scope }) {
+    const seq = [];
+    const seenSplits = new Set();
+    for (const tab of tabs) {
+      const groupId = tab.groupId || null;
+      if (groupId && splitIds.has(groupId)) {
+        if (
+          !seenSplits.has(groupId) &&
+          scope.matchSplit(
+            splitParents.get(groupId) ?? null,
+            splitWs.get(groupId) ?? null
+          )
+        ) {
+          seenSplits.add(groupId);
+          seq.push(groupId);
+        }
+        continue;
+      }
+      if (scope.matchTab(tab, groupId)) {
+        seq.push(tab.zenSyncId);
+      }
+    }
+    for (const folder of folders) {
+      if (!scope.matchFolder(folder)) {
+        continue;
+      }
+      let index = seq.length;
+      const prev = folder.prevSiblingInfo;
+      if (!prev || prev.type === "start") {
+        // No stored sibling means the folder is the first child of its
+        // container (the section rebuild on startup places content before
+        // the fake start element, so the first item has no sibling at all).
+        index = 0;
+      } else if (prev.id) {
+        const at = seq.indexOf(prev.id);
+        if (at !== -1) {
+          index = at + 1;
+        } else if (prev.type === "tab") {
+          // An unsynced tab sibling (empty placeholders, live folder items)
+          // always sits at the start of its container.
+          index = 0;
+        }
+      }
+      seq.splice(index, 0, folder.id);
+    }
+    return seq;
+  }
+
+  /**
+   * Derives the shared projection context from one sidebar collection.
+   * Syncable tabs, folders, the syncable splits and their parents and
+   * workspaces, plus the folder-membership resolver.
+   *
+   * @param {object} sidebar
+   */
+  #projectionContext(sidebar) {
+    const tabs = (sidebar.tabs || []).filter(t => this.#isSyncableTab(t));
+    const folders = (sidebar.folders || []).filter(
+      f => f?.id && !f.splitViewGroup
+    );
+    const folderIds = new Set(folders.map(f => f.id));
+    const allSplits = (sidebar.splitViewData || []).filter(g => g?.groupId);
+    const splitParents = new Map();
+    for (const entry of sidebar.folders || []) {
+      if (entry?.splitViewGroup && entry.id) {
+        splitParents.set(entry.id, entry.parentId || null);
+      }
+    }
+
+    // Only splits whose members are all synced tabs are synced themselves.
+    const syncableTabIds = new Set(tabs.map(t => t.zenSyncId));
+    const splits = allSplits.filter(
+      g =>
+        Array.isArray(g.tabs) &&
+        g.tabs.length >= 2 &&
+        g.tabs.every(id => syncableTabIds.has(id))
+    );
+    const splitIds = new Set(splits.map(g => g.groupId));
+    const splitWs = new Map();
+    for (const tab of tabs) {
+      const groupId = tab.groupId || null;
+      if (groupId && splitIds.has(groupId) && !splitWs.has(groupId)) {
+        splitWs.set(groupId, tab.zenWorkspace || null);
+      }
+    }
+    const folderOf = groupId => {
+      if (!groupId) {
+        return null;
+      }
+      if (splitIds.has(groupId)) {
+        return splitParents.get(groupId) || null;
+      }
+      return folderIds.has(groupId) ? groupId : null;
+    };
+    return { tabs, folders, splits, splitIds, splitParents, splitWs, folderOf };
+  }
+
+  /**
+   * @param {Map} map
+   * @param {object} ctx - The projection context.
+   */
+  #projectTabs(map, ctx) {
+    for (const tab of ctx.tabs) {
+      const identity = this.#tabIdentity(tab);
+      if (!identity) {
+        continue;
+      }
+      const essential = !!tab.zenEssential;
+      map.set(tab.zenSyncId, {
+        kind: RECORD_KINDS.TAB,
+        data: {
+          tabId: tab.zenSyncId,
+          url: identity.url,
+          title: identity.title,
+          icon: identity.icon,
+          containerGuid: this.guidForContextId(tab.userContextId, {
+            create: true,
+          }),
+          essential,
+          workspaceUuid: essential ? null : tab.zenWorkspace || null,
+          folderId: ctx.folderOf(tab.groupId || null),
+          staticLabel:
+            typeof tab.zenStaticLabel === "string" ? tab.zenStaticLabel : null,
+          hasStaticIcon: !!tab.zenHasStaticIcon,
+          defaultContainer: !!tab.zenDefaultUserContextId,
+        },
+      });
+    }
+  }
+
+  projections() {
+    const sidebar = lazy.ZenSessionStore.getSidebarData() || {};
+    const stamp = sidebar.lastCollected || 0;
+    if (this.#cache && this.#cache.stamp === stamp) {
+      return this.#cache.map;
+    }
+
+    const map = new Map();
+    const pending = new Set();
+    const ctx = this.#projectionContext(sidebar);
+    const { tabs, folders, splits, splitIds, splitParents, splitWs } = ctx;
+
+    for (const identity of lazy.ContextualIdentityService.getPublicIdentities()) {
+      if (!identity.name) {
+        continue;
+      }
+      const guid = this.guidForContextId(identity.userContextId, {
+        create: true,
+      });
+      if (!guid) {
+        continue;
+      }
+      map.set(guid, {
+        kind: RECORD_KINDS.CONTAINER,
+        data: {
+          guid,
+          name: identity.name,
+          icon: identity.icon || "",
+          color: identity.color || "",
+        },
+      });
+    }
+
+    const spaces = sidebar.spaces || [];
+    for (const space of spaces) {
+      if (!space?.uuid) {
+        continue;
+      }
+      const uuid = space.uuid;
+      map.set(uuid, {
+        kind: RECORD_KINDS.SPACE,
+        data: {
+          uuid,
+          name: space.name ?? "",
+          icon: space.icon ?? null,
+          theme: space.theme ?? null,
+          containerGuid: this.guidForContextId(space.containerTabId, {
+            create: true,
+          }),
+          children: this.#childSequence({
+            tabs,
+            folders,
+            splitIds,
+            splitParents,
+            splitWs,
+            scope: {
+              matchTab: (t, groupId) =>
+                !groupId &&
+                !t.zenEssential &&
+                (t.zenWorkspace || null) === uuid,
+              matchSplit: (parent, ws) => !parent && ws === uuid,
+              matchFolder: f => !f.parentId && (f.workspaceId || null) === uuid,
+            },
+          }),
+        },
+      });
+    }
+
+    for (const folder of folders) {
+      const fid = folder.id;
+      let live = null;
+      if (folder.isLiveFolder) {
+        try {
+          live = lazy.ZenLiveFoldersManager.getSyncableFolderData(fid);
+        } catch (e) {
+          console.error("ZenSpacesSync: failed to project live folder", e);
+        }
+        if (!live) {
+          pending.add(fid);
+          continue;
+        }
+      }
+      map.set(fid, {
+        kind: RECORD_KINDS.FOLDER,
+        data: {
+          folderId: fid,
+          name: folder.name ?? "",
+          icon: folder.userIcon || null,
+          workspaceUuid: folder.workspaceId || null,
+          parentFolderId: folder.parentId || null,
+          live,
+          children: this.#childSequence({
+            tabs,
+            folders,
+            splitIds,
+            splitParents,
+            splitWs,
+            scope: {
+              matchTab: (t, groupId) => groupId === fid,
+              matchSplit: parent => parent === fid,
+              matchFolder: f => f.parentId === fid,
+            },
+          }),
+        },
+      });
+    }
+
+    this.#projectTabs(map, ctx);
+
+    for (const split of splits) {
+      map.set(split.groupId, {
+        kind: RECORD_KINDS.SPLIT,
+        data: {
+          splitId: split.groupId,
+          gridType: split.gridType || "grid",
+          tabs: [...split.tabs],
+          workspaceUuid: splitWs.get(split.groupId) ?? null,
+          folderId: splitParents.get(split.groupId) || null,
+        },
+      });
+    }
+
+    if (spaces.length) {
+      const essentials = {};
+      for (const tab of tabs) {
+        if (!tab.zenEssential) {
+          continue;
+        }
+        const key =
+          this.guidForContextId(tab.userContextId, { create: true }) ||
+          "default";
+        (essentials[key] ||= []).push(tab.zenSyncId);
+      }
+      map.set(LAYOUT_RECORD_ID, {
+        kind: RECORD_KINDS.LAYOUT,
+        data: {
+          spaces: spaces.map(s => s.uuid).filter(Boolean),
+          essentials,
+        },
+      });
+    }
+
+    this.#cache = { stamp, map, pending };
+    return map;
+  }
+
+  /**
+   * Ids that are locally present but deliberately not projected this cycle
+   * (live folders whose provider config isn't available yet). The diff must
+   * not read their absence as a deletion.
+   */
+  #pendingIds() {
+    this.projections();
+    return this.#cache.pending;
+  }
+
+  #digestCache = null;
+
+  /**
+   * Digests of all current projections. Change detection runs several times per
+   * sync cycle (tracker observe, changed-id computation, upload bookkeeping)
+   * and only needs to hash again after a fresh sidebar collection.
+   */
+  #digestAll() {
+    const map = this.projections();
+    if (this.#digestCache?.map === map) {
+      return this.#digestCache.digests;
+    }
+    const digests = new Map();
+    for (const [id, projected] of map) {
+      digests.set(id, recordDigest(projected.kind, projected.data));
+    }
+    this.#digestCache = { map, digests };
+    return digests;
+  }
+
+  /* Mark: engine-facing API */
+
+  getAllRecordIds() {
+    const ids = {};
+    for (const id of this.projections().keys()) {
+      ids[id] = true;
+    }
+    return ids;
+  }
+
+  itemExists(id) {
+    return this.projections().has(id);
+  }
+
+  projectRecord(id) {
+    return this.projections().get(id) ?? null;
+  }
+
+  /**
+   * Changes = diff between the current projections and the last state the
+   * server acknowledged. Ids present locally with different content are
+   * modified; ids only present in the uploaded snapshot are deletions.
+   */
+  computeChangedIDs() {
+    const uploaded = this.#data().uploaded;
+    const current = this.#digestAll();
+    const pending = this.#pendingIds();
+    const now = Date.now() / 1000;
+    const changes = {};
+    for (const [id, digest] of current) {
+      if (uploaded[id] !== digest) {
+        changes[id] = now;
+      }
+    }
+    for (const id of Object.keys(uploaded)) {
+      if (!current.has(id) && !pending.has(id)) {
+        changes[id] = now;
+      }
+    }
+    if (lazy.syncDebug && Object.keys(changes).length) {
+      const map = this.projections();
+      syncLog(
+        "outgoing diff:",
+        Object.keys(changes).map(id =>
+          current.has(id) ? `${map.get(id)?.kind} ${id}` : `TOMBSTONE ${id}`
+        )
+      );
+    }
+    return changes;
+  }
+
+  hasPendingChanges() {
+    const uploaded = this.#data().uploaded;
+    const current = this.#digestAll();
+    const pending = this.#pendingIds();
+    for (const [id, digest] of current) {
+      if (uploaded[id] !== digest) {
+        return true;
+      }
+    }
+    for (const id of Object.keys(uploaded)) {
+      if (!current.has(id) && !pending.has(id)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Called after records were successfully uploaded. Remember exactly what
+   * the server now holds for them.
+   *
+   * @param {Array<string>} ids
+   */
+  markUploaded(ids) {
+    const data = this.#data();
+    const current = this.#digestAll();
+    for (const id of ids) {
+      if (current.has(id)) {
+        data.uploaded[id] = current.get(id);
+      } else {
+        delete data.uploaded[id];
+      }
+    }
+    if (lazy.syncDebug && ids.length) {
+      syncLog(
+        "server acknowledged upload:",
+        ids.map(id => (current.has(id) ? id : `${id} (tombstone)`))
+      );
+    }
+    this.#file.saveSoon();
+  }
+
+  /**
+   * Called after an incoming record was applied locally. Storing the
+   * incoming payload as the uploaded state means a faithful local
+   * materialization produces no re-upload, while a divergent one re-uploads
+   * the local truth (self-healing).
+   *
+   * @param {string} id
+   * @param {?object} cleartext - null for tombstones.
+   */
+  noteApplied(id, cleartext) {
+    const data = this.#data();
+    if (!cleartext) {
+      delete data.uploaded[id];
+    } else {
+      data.uploaded[id] = recordDigest(cleartext.kind, cleartext.data);
+    }
+    syncLog(
+      `acknowledged incoming ${cleartext ? cleartext.kind : "tombstone"} ${id}`
+    );
+    this.#file.saveSoon();
+  }
+}
+
+export const ZenSpacesSyncModel = new nsZenSpacesSyncModel();
--- a/src/zen/sync/ZenSyncManager.sys.mjs
+++ b/src/zen/sync/ZenSyncManager.sys.mjs
@@ -1,160 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-const lazy = {};
-
-ChromeUtils.defineESModuleGetters(lazy, {
-  ZenSessionStore: "resource:///modules/zen/ZenSessionManager.sys.mjs",
-  ContextualIdentityService:
-    "resource://gre/modules/ContextualIdentityService.sys.mjs",
-  ZenWindowSync: "resource:///modules/zen/ZenWindowSync.sys.mjs",
-});
-
-function normalizeUserContextId(value) {
-  const normalized = typeof value === "string" ? Number(value) : value;
-  if (!Number.isSafeInteger(normalized) || normalized <= 0) {
-    return null;
-  }
-  return normalized;
-}
-
-class ZenSyncManager {
-  getSidebarData() {
-    return lazy.ZenSessionStore.getSidebarData();
-  }
-
-  /**
-   * Whether to ignore changes to items. This is used to prevent
-   * infinite loops when applying incoming sync changes.
-   *
-   * @type {boolean}
-   */
-  #ignoreChanges = false;
-
-  #changedItems = new Map();
-
-  markItemChanged(item) {
-    if (item.type && item.id && !this.#ignoreChanges) {
-      const key = `${item.type}~${item.id}`;
-      this.#changedItems.set(key, { type: item.type, id: item.id });
-    }
-  }
-
-  #getChangedItems() {
-    return Array.from(this.#changedItems.values());
-  }
-
-  #clearChangedItems() {
-    this.#changedItems.clear();
-  }
-
-  notifyAboutChanges() {
-    const changedItems = this.#getChangedItems();
-
-    for (const item of changedItems) {
-      Services.obs.notifyObservers(
-        { wrappedJSObject: item },
-        "zen-workspace-item-changed"
-      );
-    }
-    this.#clearChangedItems();
-  }
-
-  async applyIncomingBatch(pulled, removals) {
-    try {
-      this.#ignoreChanges = true;
-      this.#applyIncomingContainers(
-        pulled.containers || [],
-        removals.containers || []
-      );
-
-      const win = lazy.ZenWindowSync.firstSyncedWindow;
-      if (win?.gZenWorkspaces) {
-        await win.gZenWorkspaces._applySyncChanges(pulled, removals);
-      }
-    } catch (e) {
-      console.error("ZenSyncManager: Failed to apply incoming sync data:", e);
-      throw e;
-    } finally {
-      this.#ignoreChanges = false;
-    }
-  }
-
-  #applyIncomingContainers(pulledContainers, removedContainers) {
-    const localContainersById = new Map(
-      lazy.ContextualIdentityService.getPublicIdentities().map(container => [
-        container.userContextId,
-        container,
-      ])
-    );
-
-    for (const container of pulledContainers) {
-      if (!container.name) {
-        continue;
-      }
-
-      const userContextId = normalizeUserContextId(container.userContextId);
-      if (userContextId === null) {
-        console.warn(
-          "ZenSyncManager: Ignoring incoming container with invalid userContextId",
-          { container }
-        );
-        continue;
-      }
-
-      const existsLocally = localContainersById.has(userContextId);
-
-      if (existsLocally) {
-        lazy.ContextualIdentityService.update(
-          userContextId,
-          container.name,
-          container.icon,
-          container.color
-        );
-        continue;
-      }
-
-      const createdIdentity = lazy.ContextualIdentityService.create(
-        container.name,
-        container.icon,
-        container.color,
-        userContextId
-      );
-      if (createdIdentity) {
-        localContainersById.set(createdIdentity.userContextId, createdIdentity);
-      }
-      if (createdIdentity && createdIdentity.userContextId !== userContextId) {
-        console.warn("ZenSyncManager: Container sync created unexpected ID", {
-          requestedId: userContextId,
-          createdId: createdIdentity.userContextId,
-          name: container.name,
-        });
-      }
-    }
-
-    for (const container of removedContainers) {
-      const userContextId = normalizeUserContextId(container.userContextId);
-      if (userContextId === null) {
-        console.warn(
-          "ZenSyncManager: Ignoring container removal with invalid userContextId",
-          { container }
-        );
-        continue;
-      }
-
-      if (!localContainersById.has(userContextId)) {
-        continue;
-      }
-
-      try {
-        lazy.ContextualIdentityService.remove(userContextId);
-        localContainersById.delete(userContextId);
-      } catch {
-        // Container may already be gone locally.
-      }
-    }
-  }
-}
-
-export const ZenSyncStore = new ZenSyncManager();
--- a/src/zen/sync/ZenWorkspacesSync.sys.mjs
+++ b/src/zen/sync/ZenWorkspacesSync.sys.mjs
@@ -1,404 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-import {
-  Store,
-  SyncEngine,
-  Tracker,
-} from "resource://services-sync/engines.sys.mjs";
-import { CryptoWrapper } from "resource://services-sync/record.sys.mjs";
-import { SCORE_INCREMENT_XLARGE } from "resource://services-sync/constants.sys.mjs";
-
-const lazy = {};
-
-ChromeUtils.defineESModuleGetters(lazy, {
-  ZenSyncStore: "resource:///modules/zen/ZenSyncManager.sys.mjs",
-  ContextualIdentityService:
-    "resource://gre/modules/ContextualIdentityService.sys.mjs",
-});
-
-const RECORD_ID_PREFIX_BY_TYPE = Object.freeze({
-  space: "s",
-  container: "c",
-});
-
-const RECORD_TYPE_BY_PREFIX = Object.freeze({
-  s: "space",
-  c: "container",
-});
-
-/**
- * Sync record wrapper for workspace and container items stored in the
- * Workspaces engine collection.
- */
-export class ZenWorkspacesRecord extends CryptoWrapper {
-  _logName = "Sync.Record.ZenSpaces";
-}
-
-ZenWorkspacesRecord.prototype.type = "spaces";
-
-function parseRecordId(id) {
-  const sep = id.indexOf("~");
-  if (sep === -1) {
-    return null;
-  }
-  const prefix = id.slice(0, sep);
-  const key = id.slice(sep + 1);
-  return { type: RECORD_TYPE_BY_PREFIX[prefix] || prefix, key };
-}
-
-function createRecordId(type, id) {
-  const prefix = RECORD_ID_PREFIX_BY_TYPE[type];
-  if (!prefix) {
-    throw new Error(`Unknown Spaces Sync record type: ${type}`);
-  }
-  return `${prefix}~${id}`;
-}
-
-function normalizeUserContextId(value) {
-  const normalized = typeof value === "string" ? Number(value) : value;
-  if (!Number.isSafeInteger(normalized) || normalized <= 0) {
-    return null;
-  }
-  return normalized;
-}
-
-/**
- * Strips the sync-envelope fields (`id` and `type`) from incoming record data
- * and restores the item's real identity key where needed
- *
- * @param {object} data
- */
-function stripSyncFields(data) {
-  const rest = { ...data };
-  delete rest.id;
-  delete rest.type;
-  return rest;
-}
-
-/**
- * Sync store implementation that serializes local workspace and container
- * state into records and applies incoming remote changes.
- */
-class ZenWorkspacesStore extends Store {
-  constructor(name, engine) {
-    super(name, engine);
-  }
-
-  async getAllIDs() {
-    const ids = {};
-    const sidebar = lazy.ZenSyncStore.getSidebarData();
-
-    for (const space of sidebar.spaces || []) {
-      if (space.uuid) {
-        ids[createRecordId("space", space.uuid)] = true;
-      }
-    }
-
-    for (const c of lazy.ContextualIdentityService.getPublicIdentities()) {
-      ids[createRecordId("container", c.userContextId)] = true;
-    }
-
-    return ids;
-  }
-
-  async itemExists(id) {
-    const parsed = parseRecordId(id);
-    if (!parsed) {
-      return false;
-    }
-    const sidebar = lazy.ZenSyncStore.getSidebarData();
-
-    switch (parsed.type) {
-      case "space":
-        return (sidebar.spaces || []).some(s => s.uuid === parsed.key);
-      case "container":
-        return lazy.ContextualIdentityService.getPublicIdentities().some(
-          c => String(c.userContextId) === parsed.key
-        );
-      default:
-        return false;
-    }
-  }
-
-  async createRecord(id, collection) {
-    const record = new ZenWorkspacesRecord(collection, id);
-    const parsed = parseRecordId(id);
-    if (!parsed) {
-      record.deleted = true;
-      return record;
-    }
-
-    const sidebar = lazy.ZenSyncStore.getSidebarData();
-
-    switch (parsed.type) {
-      case "space": {
-        const spaces = sidebar.spaces || [];
-        const idx = spaces.findIndex(s => s.uuid === parsed.key);
-        if (idx === -1) {
-          record.deleted = true;
-          return record;
-        }
-        const rest = { ...spaces[idx] };
-        delete rest.syncStatus;
-        record.cleartext = { id, type: "space", ...rest, position: idx };
-        break;
-      }
-
-      case "container": {
-        const container =
-          lazy.ContextualIdentityService.getPublicIdentities().find(
-            c => String(c.userContextId) === parsed.key
-          );
-        if (!container) {
-          record.deleted = true;
-          return record;
-        }
-        record.cleartext = {
-          id,
-          type: "container",
-          userContextId: container.userContextId,
-          name: container.name,
-          icon: container.icon,
-          color: container.color,
-        };
-        break;
-      }
-
-      default:
-        record.deleted = true;
-    }
-
-    return record;
-  }
-
-  async applyIncomingBatch(records, _countTelemetry) {
-    const pulled = { spaces: [], containers: [] };
-    const removals = { spaces: [], containers: [] };
-
-    for (const record of records) {
-      if (record.deleted) {
-        this._collectRemoval(record.id, removals);
-        continue;
-      }
-      const data = record.cleartext;
-      if (!data?.type) {
-        continue;
-      }
-      const clean = stripSyncFields(data);
-      switch (data.type) {
-        case "space":
-          pulled.spaces.push(clean);
-          break;
-        case "container":
-          pulled.containers.push(clean);
-          break;
-      }
-    }
-
-    // Suppress change tracking while applying incoming data to prevent
-    // feedback loops where applied items get re-uploaded immediately.
-    this.engine._tracker.ignoreAll = true;
-    try {
-      await lazy.ZenSyncStore.applyIncomingBatch(pulled, removals);
-    } finally {
-      this.engine._tracker.ignoreAll = false;
-    }
-    return [];
-  }
-
-  _collectRemoval(id, removals) {
-    const parsed = parseRecordId(id);
-    if (!parsed) {
-      return;
-    }
-    switch (parsed.type) {
-      case "space":
-        removals.spaces.push({ uuid: parsed.key });
-        break;
-      case "container": {
-        const userContextId = normalizeUserContextId(parsed.key);
-        if (userContextId === null) {
-          console.warn(
-            "ZenWorkspacesStore: Ignoring container removal with invalid userContextId",
-            { id }
-          );
-          break;
-        }
-        removals.containers.push({ userContextId });
-        break;
-      }
-    }
-  }
-
-  async create(record) {
-    await this._applySingle(record);
-  }
-
-  async update(record) {
-    await this._applySingle(record);
-  }
-
-  async _applySingle(record) {
-    this.engine._tracker.ignoreAll = true;
-    try {
-      if (record.deleted) {
-        const removals = { spaces: [], containers: [] };
-        this._collectRemoval(record.id, removals);
-        await lazy.ZenSyncStore.applyIncomingBatch(
-          { spaces: [], containers: [] },
-          removals
-        );
-        return;
-      }
-      const data = record.cleartext;
-      if (!data?.type) {
-        return;
-      }
-      const clean = stripSyncFields(data);
-      const pulled = { spaces: [], containers: [] };
-      switch (data.type) {
-        case "space":
-          pulled.spaces.push(clean);
-          break;
-        case "container":
-          pulled.containers.push(clean);
-          break;
-      }
-      await lazy.ZenSyncStore.applyIncomingBatch(pulled, {
-        spaces: [],
-        containers: [],
-      });
-    } finally {
-      this.engine._tracker.ignoreAll = false;
-    }
-  }
-
-  async remove() {
-    // No-op: never delete user data on wipe
-  }
-
-  async wipe() {
-    // No-op: never delete user data on wipe
-  }
-
-  changeItemID() {
-    // No-op
-  }
-}
-
-/**
- * Sync tracker that watches workspace and contextual identity observers and
- * marks the corresponding record IDs as changed.
- */
-class ZenWorkspacesTracker extends Tracker {
-  #changedIDs = {};
-  #ignoreAll = false;
-
-  get ignoreAll() {
-    return this.#ignoreAll;
-  }
-
-  set ignoreAll(value) {
-    this.#ignoreAll = value;
-  }
-
-  onStart() {
-    Services.obs.addObserver(this, "zen-workspace-item-changed");
-    Services.obs.addObserver(this, "contextual-identity-created");
-    Services.obs.addObserver(this, "contextual-identity-updated");
-    Services.obs.addObserver(this, "contextual-identity-deleted");
-  }
-
-  onStop() {
-    Services.obs.removeObserver(this, "zen-workspace-item-changed");
-    Services.obs.removeObserver(this, "contextual-identity-created");
-    Services.obs.removeObserver(this, "contextual-identity-updated");
-    Services.obs.removeObserver(this, "contextual-identity-deleted");
-  }
-
-  observe(subject, topic, _data) {
-    if (this.#ignoreAll) {
-      return;
-    }
-    if (topic === "zen-workspace-item-changed") {
-      const type = subject?.wrappedJSObject?.type;
-      const id = subject?.wrappedJSObject?.id;
-      if (type && id) {
-        this._trackChange({ type, id });
-      }
-    } else if (topic.startsWith("contextual-identity-")) {
-      const id = subject?.wrappedJSObject?.userContextId;
-      if (id && normalizeUserContextId(id) !== null) {
-        this._trackChange({ type: "container", id });
-      }
-    }
-  }
-
-  _trackChange(data) {
-    if (data.type && data.id) {
-      const id = createRecordId(data.type, data.id);
-      this.#changedIDs[id] = Date.now() / 1000;
-      this.score += SCORE_INCREMENT_XLARGE;
-    }
-  }
-
-  async getChangedIDs() {
-    return { ...this.#changedIDs };
-  }
-
-  async addChangedID(id, when) {
-    this.#changedIDs[id] = when;
-    return true;
-  }
-
-  async removeChangedID(...ids) {
-    for (const id of ids) {
-      delete this.#changedIDs[id];
-    }
-    return true;
-  }
-
-  clearChangedIDs() {
-    this.#changedIDs = {};
-  }
-}
-
-/**
- * Sync engine entrypoint that wires the Workspaces record, store, and tracker
- * implementations into Firefox Sync.
- */
-export class ZenWorkspacesEngine extends SyncEngine {
-  static get name() {
-    return "Spaces";
-  }
-
-  constructor(service) {
-    super("Spaces", service);
-  }
-
-  get _storeObj() {
-    return ZenWorkspacesStore;
-  }
-
-  get _trackerObj() {
-    return ZenWorkspacesTracker;
-  }
-
-  get _recordObj() {
-    return ZenWorkspacesRecord;
-  }
-
-  get version() {
-    return 2;
-  }
-
-  get syncPriority() {
-    return 8;
-  }
-
-  get allowSkippedRecord() {
-    return false;
-  }
-}
--- a/src/zen/sync/moz.build
+++ b/src/zen/sync/moz.build
@@ -3,6 +3,7 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.

 EXTRA_JS_MODULES.zen += [
-  "ZenSyncManager.sys.mjs",
-  "ZenWorkspacesSync.sys.mjs",
+    "ZenSpacesSync.sys.mjs",
+    "ZenSpacesSyncApplier.sys.mjs",
+    "ZenSpacesSyncModel.sys.mjs",
 ]
--- a/src/zen/tabs/ZenPinnedTabManager.mjs
+++ b/src/zen/tabs/ZenPinnedTabManager.mjs
@@ -503,7 +503,7 @@ class nsZenPinnedTabManager extends nsZenDOMOperatedFeature {
    }
  }

-  addToEssentials(tab) {
+  addToEssentials(tab, { replicating = false } = {}) {
    // eslint-disable-next-line no-nested-ternary
    const tabs = tab
      ? // if it's already an array, dont make it [tab]
@@ -518,7 +518,12 @@ class nsZenPinnedTabManager extends nsZenDOMOperatedFeature {
      // eslint-disable-next-line no-shadow
      let tab = tabs[i];
      const section = gZenWorkspaces.getEssentialsSection(tab);
-      if (!this.canEssentialBeAdded(tab)) {
+      // canEssentialBeAdded gates user-initiated adds on the *active* space's
+      // container. A replicated add mirrors a decision already made in another
+      // window or on another device, always into the tab's own container
+      // section.
+      if (!replicating && !this.canEssentialBeAdded(tab)) {
+        this.log(`addToEssentials rejected for ${tab.id}`);
        movedAll = false;
        continue;
      }
@@ -570,6 +575,13 @@ class nsZenPinnedTabManager extends nsZenDOMOperatedFeature {
    for (let i = 0; i < tabs.length; i++) {
      // eslint-disable-next-line no-shadow
      const tab = tabs[i];
+      if (this._canLog) {
+        // eslint-disable-next-line no-console
+        console.trace(
+          `ZenPinnedTabManager: removing tab ${tab.id} from essentials ` +
+            `(unpin=${unpin})`
+        );
+      }
      tab.removeAttribute("zen-essential");
      if (
        gZenWorkspaces.workspaceEnabled &&
--- a/src/zen/tabs/zen-tabs/vertical-tabs-topbuttons-fix.css
+++ b/src/zen/tabs/zen-tabs/vertical-tabs-topbuttons-fix.css
@@ -4,6 +4,7 @@
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

+/* stylelint-disable-next-line stylelint-plugin-mozilla/no-has-selector */
 &:not([zen-compact-animating])
  #zen-sidebar-top-buttons:not(:has(#zen-sidebar-top-buttons-customization-target > *:not(#zen-sidebar-top-buttons-separator), .titlebar-buttonbox-container)) {
  max-height: 0 !important;
--- a/src/zen/tabs/zen-tabs/vertical-tabs.css
+++ b/src/zen/tabs/zen-tabs/vertical-tabs.css
@@ -100,9 +100,10 @@
    width: -moz-available !important;
  }

+  /* stylelint-disable-next-line stylelint-plugin-mozilla/no-has-selector */
  & #urlbar-container[breakout="true"]:has(#urlbar[zen-floating-urlbar="true"]) {
    --urlbar-container-height: 36px !important;
-    --urlbar-height: 38px !important;
+    --urlbar-height: 36px !important;
  }

  & #nav-bar {
@@ -225,19 +226,9 @@
   ========================================================================== */
 #navigator-toolbox {
  /* Define theme variables, including platform specifics for native look */
-  --border-radius-medium: 10px;
-  --tab-border-radius: 6px;
  --zen-toolbox-min-width: 1px;
-
-  @media (-moz-platform: windows) {
-    --border-radius-medium: 6px;
-    --tab-border-radius: 4px;
-  }
-
-  @media (-moz-platform: macos) {
-    --border-radius-medium: 12px;
-    --tab-border-radius: 8px;
-  }
+  --border-radius-medium: 14px;
+  --tab-border-radius: 8px;

  min-width: var(--zen-toolbox-min-width);
  margin-top: 0 !important;
@@ -329,6 +320,7 @@
      display: none;
    }

+    /* stylelint-disable-next-line stylelint-plugin-mozilla/no-has-selector */
    :root:not([zen-renaming-tab="true"])
    #tabbrowser-tabs:not([movingtab])
    &:active:not(:has(.tab-content > image:active)) {
@@ -538,8 +530,7 @@

    :root[zen-single-toolbar="true"]:not([zen-has-empty-tab="true"]) & {
      & #urlbar:not([breakout-extend]) .urlbar-input-container {
-        padding-left: 8px;
-        padding-right: 4px;
+        padding-inline: 4px;
      }
    }
  }
@@ -1209,6 +1200,8 @@
        background-position: center;
        fill: currentColor;
        -moz-context-properties: fill, fill-opacity;
+        /* stylelint-disable-next-line property-no-unknown */
+        corner-shape: superellipse(var(--zen-squircle-value));
      }

      background: transparent;
@@ -1233,6 +1226,8 @@
        z-index: 0;
        content: "";
        transition: background 0.1s ease-in-out;
+        /* stylelint-disable-next-line property-no-unknown */
+        corner-shape: superellipse(var(--zen-squircle-value));
      }
    }

@@ -1341,7 +1336,7 @@

 #tabs-newtab-button:not([in-urlbar="true"]) label,
 .zen-current-workspace-indicator-name {
-  opacity: 0.7;
+  color: color-mix(in srgb, currentColor 70%, transparent);
 }

 /* stylelint-disable-next-line media-query-no-invalid */
--- a/src/zen/tests/manifest.toml
+++ b/src/zen/tests/manifest.toml
@@ -3,6 +3,36 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.

+[alerts]
+source = "browser/base/content/test/alerts"
+is_direct_path = true
+
+[backforward]
+source = "browser/base/content/test/backforward"
+is_direct_path = true
+
+[caps]
+source = "browser/base/content/test/caps"
+is_direct_path = true
+
+[gesture]
+source = "browser/base/content/test/gesture"
+is_direct_path = true
+
+[gesture.replace-manifest]
+"[DEFAULT]" = '''[DEFAULT]
+prefs = [
+  "zen.window-sync.enabled=false",
+]'''
+
+[linkHandling]
+source = "browser/base/content/test/linkHandling"
+is_direct_path = true
+disable = [
+  # Glance opens with alt+click, firefox doesnt know that.
+  "browser_javascript_links.js",
+]
+
 [readermode]
 source = "toolkit/components/reader/tests/browser"
 is_direct_path = true
@@ -13,10 +43,88 @@ disable = [
  "browser_readerMode_colorSchemePref.js",
 ]

+[remote-settings]
+source = "services/settings/test/unit"
+is_direct_path = true
+xpcshell = true
+
+[remote-settings.replace-manifest]
+"../../../" = "../../../../services/"
+
 [safebrowsing]
 source = "browser/components/safebrowsing/content/test"
 is_direct_path = true

+[services-crypto]
+source = "services/crypto/tests/unit"
+is_direct_path = true
+xpcshell = true
+
+[services-crypto.replace-manifest]
+"../../../" = "../../../../services/"
+
+[sessionstore]
+source = "browser/components/sessionstore/test"
+is_direct_path = true
+disable = [
+  "browser_1933485_tab_groups_history.js",
+  "browser_1953801_tab_groups_history_close_other.js",
+  "browser_aboutSessionRestore.js",
+  "browser_bfcache_telemetry.js",
+  "browser_closedId.js",
+  "browser_closed_objects_changed_notifications_tabs.js",
+  "browser_closed_objects_changed_notifications_windows.js",
+  "browser_closed_tabs_closed_windows.js",
+  "browser_closed_tabs_windows.js",
+  "browser_cookies_partitioned.js",
+  "browser_crashedTabs.js",
+  "browser_dying_cache.js",
+  "browser_firefoxView_restore.js",
+  "browser_firefoxView_selected_restore.js",
+  "browser_forget_closed_tab_window_byId.js",
+  "browser_movePendingTabToNewWindow.js",
+  "browser_newtab_userTypedValue.js",
+  "browser_pinned_tabs.js",
+  "browser_purge_domaindata.js",
+  "browser_reopen_all_windows.js",
+  "browser_restoreLastActionCorrectOrder.js",
+  "browser_restoreLastClosedTabOrWindowOrSession.js",
+  "browser_restore_container_tabs_oa.js",
+  "browser_restore_tabless_window.js",
+  "browser_restore_verticalPinnedTabs.js",
+  "browser_restored_window_features.js",
+  "browser_scrollPositions.js",
+  "browser_scrollPositionsReaderMode.js",
+  "browser_searchModeSwitcher_restore.js",
+  "browser_speculative_connect.js",
+  "browser_splitview_integer_ids.js",
+  "browser_splitview_restore_in_closed_window.js",
+  "browser_splitview_string_migration.js",
+  "browser_swapDocShells.js",
+  "browser_tab_groups_restore_closed_in_closed_window.js",
+  "browser_tab_groups_restore_closed_in_open_window.js",
+  "browser_tab_groups_restore_closed_many_tabs.js",
+  "browser_tab_groups_closed.js",
+  "browser_tab_groups_restore_multiple.js",
+  "browser_tab_groups_restore_saved.js",
+  "browser_tab_groups_restore_simple.js",
+  "browser_tab_groups_save_on_removeAllTabsBut.js",
+  "browser_tab_groups_save_on_removeTabsToTheEnd.js",
+  "browser_tab_groups_save_on_removeTabsToTheStart.js",
+  "browser_tab_groups_save_on_window_close.js",
+  "browser_tab_groups_state.js",
+  "browser_tab_groups_undo.js",
+  "browser_tab_label_during_restore.js",
+  "browser_undoCloseById.js",
+  "browser_urlbarSearchMode.js",
+  "browser_windowStateContainer.js",
+  "browser_wireframe_basic.js",
+]
+
+[sessionstore.replace-manifest]
+'prefs = [' = '''prefs = [
+  "zen.window-sync.enabled=false",'''
+
 [shell]
 source = "browser/components/shell/test"
 is_direct_path = true
@@ -25,6 +133,15 @@ disable = [
  "browser_setDesktopBackgroundPreview.js",
 ]

+[sync]
+source = "services/sync/tests/unit"
+is_direct_path = true
+xpcshell = true
+
+[sync.replace-manifest]
+"../../../" = "../../../../services/"
+'"identity.fxaccounts.enabled=true"' = '"identity.fxaccounts.enabled=true", "browser.formfill.enable=true"'
+
 [tabMediaIndicator]
 source = "browser/components/tabbrowser/test/browser/tabMediaIndicator"
 is_direct_path = true
@@ -34,3 +151,10 @@ source = "toolkit/components/tooltiptext"
 disable = [
  "browser_input_file_tooltips.js",
 ]
+
+[zoom]
+source = "browser/base/content/test/zoom"
+is_direct_path = true
+
+[zoom.replace-manifest]
+"../general/" = "../../../../browser/base/content/test/general/"
--- a/src/zen/tests/mochitests/alerts/browser.toml
+++ b/src/zen/tests/mochitests/alerts/browser.toml
@@ -0,0 +1,32 @@
+[DEFAULT]
+support-files = [
+  "head.js",
+  "file_dom_notifications.html",
+]
+
+["browser_notification_close.js"]
+https_first_disabled = true
+skip-if = [
+  "os == 'win'", # Bug 1227785
+]
+
+["browser_notification_do_not_disturb.js"]
+https_first_disabled = true
+
+["browser_notification_open_settings.js"]
+https_first_disabled = true
+skip-if = [
+  "os == 'win'", # Bug 1411118
+]
+
+["browser_notification_remove_permission.js"]
+https_first_disabled = true
+skip-if = [
+  "os == 'win'", # Bug 1411118
+]
+
+["browser_notification_tab_switching.js"]
+https_first_disabled = true
+skip-if = [
+  "os == 'win'", # Bug 1243263
+]
--- a/src/zen/tests/mochitests/alerts/browser_notification_close.js
+++ b/src/zen/tests/mochitests/alerts/browser_notification_close.js
@@ -0,0 +1,78 @@
+"use strict";
+
+const { PlacesTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/PlacesTestUtils.sys.mjs"
+);
+
+const { PermissionTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/PermissionTestUtils.sys.mjs"
+);
+
+let notificationURL =
+  "https://example.org/browser/browser/base/content/test/alerts/file_dom_notifications.html";
+
+add_task(async function test_notificationClose() {
+  await addNotificationPermission(notificationURL);
+
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: notificationURL,
+    },
+    async function dummyTabTask(aBrowser) {
+      await openNotification(aBrowser, "showNotification2");
+
+      info("Notification alert showing");
+
+      let alertWindow = Services.wm.getMostRecentWindow("alert:alert");
+      if (!alertWindow) {
+        ok(true, "Notifications don't use XUL windows on all platforms.");
+        await closeNotification(aBrowser);
+        return;
+      }
+
+      let alertTitleLabel =
+        alertWindow.document.getElementById("alertTitleLabel");
+      is(
+        alertTitleLabel.value,
+        "Test title",
+        "Title text of notification should be present"
+      );
+      let alertTextLabel =
+        alertWindow.document.getElementById("alertTextLabel");
+      is(
+        alertTextLabel.textContent,
+        "Test body 2",
+        "Body text of notification should be present"
+      );
+
+      let alertCloseButton = alertWindow.document.querySelector(".close-icon");
+      is(alertCloseButton.localName, "toolbarbutton", "close button found");
+      let promiseBeforeUnloadEvent = BrowserTestUtils.waitForEvent(
+        alertWindow,
+        "beforeunload"
+      );
+      let closedTime = alertWindow.Date.now();
+      alertCloseButton.click();
+      info("Clicked on close button");
+      await promiseBeforeUnloadEvent;
+
+      ok(true, "Alert should close when the close button is clicked");
+      let currentTime = alertWindow.Date.now();
+      // The notification will self-close at 12 seconds, so this checks
+      // that the notification closed before the timeout.
+      Assert.less(
+        currentTime - closedTime,
+        5000,
+        "Close requested at " +
+          closedTime +
+          ", actually closed at " +
+          currentTime
+      );
+    }
+  );
+});
+
+add_task(async function cleanup() {
+  PermissionTestUtils.remove(notificationURL, "desktop-notification");
+});
--- a/src/zen/tests/mochitests/alerts/browser_notification_do_not_disturb.js
+++ b/src/zen/tests/mochitests/alerts/browser_notification_do_not_disturb.js
@@ -0,0 +1,159 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Tests that notifications can be silenced using nsIAlertsDoNotDisturb
+ * on systems where that interface and its methods are implemented for
+ * the nsIAlertService.
+ */
+
+const ALERT_SERVICE = Cc["@mozilla.org/alerts-service;1"]
+  .getService(Ci.nsIAlertsService)
+  .QueryInterface(Ci.nsIAlertsDoNotDisturb);
+
+const PAGE =
+  "https://example.org/browser/browser/base/content/test/alerts/file_dom_notifications.html";
+
+// The amount of time in seconds that we will wait for a notification
+// to show up before we decide that it's not coming.
+const NOTIFICATION_TIMEOUT_SECS = 2000;
+
+add_setup(async function () {
+  await addNotificationPermission(PAGE);
+});
+
+/**
+ * Test that the manualDoNotDisturb attribute can prevent
+ * notifications from appearing.
+ */
+add_task(async function test_manualDoNotDisturb() {
+  try {
+    // Only run the test if the do-not-disturb
+    // interface has been implemented.
+    ALERT_SERVICE.manualDoNotDisturb;
+    ok(true, "Alert service implements do-not-disturb interface");
+  } catch (e) {
+    ok(
+      true,
+      "Alert service doesn't implement do-not-disturb interface, exiting test"
+    );
+    return;
+  }
+
+  // In the event that something goes wrong during this test, make sure
+  // we put the attribute back to the default setting when this test file
+  // exits.
+  registerCleanupFunction(() => {
+    ALERT_SERVICE.manualDoNotDisturb = false;
+  });
+
+  // Make sure that do-not-disturb is not enabled before we start.
+  ok(
+    !ALERT_SERVICE.manualDoNotDisturb,
+    "Alert service should not be disabled when test starts"
+  );
+
+  await BrowserTestUtils.withNewTab(PAGE, async browser => {
+    await openNotification(browser, "showNotification2");
+
+    info("Notification alert showing");
+
+    let alertWindow = Services.wm.getMostRecentWindow("alert:alert");
+
+    // For now, only the XUL alert backend implements the manualDoNotDisturb
+    // method for nsIAlertsDoNotDisturb, so we expect there to be a XUL alert
+    // window. If the method gets implemented by native backends in the future,
+    // we'll probably want to branch here and set the manualDoNotDisturb
+    // attribute manually.
+    ok(alertWindow, "Expected a XUL alert window.");
+
+    // We're using the XUL notification backend. This means that there's
+    // a menuitem for enabling manualDoNotDisturb. We exercise that
+    // menuitem here.
+    let doNotDisturbMenuItem = alertWindow.document.getElementById(
+      "doNotDisturbMenuItem"
+    );
+    is(doNotDisturbMenuItem.localName, "menuitem", "menuitem found");
+
+    let unloadPromise = BrowserTestUtils.waitForEvent(
+      alertWindow,
+      "beforeunload"
+    );
+
+    doNotDisturbMenuItem.click();
+    info("Clicked on do-not-disturb menuitem");
+    await unloadPromise;
+
+    // At this point, we should be configured to not display notifications
+    // to the user.
+    ok(
+      ALERT_SERVICE.manualDoNotDisturb,
+      "Alert service should be disabled after clicking menuitem"
+    );
+
+    // The notification should not appear, but there is no way from the
+    // client-side to know that it was blocked, except for waiting some time
+    // and realizing that the "onshow" event never fired.
+    await Assert.rejects(
+      openNotification(browser, "showNotification2", NOTIFICATION_TIMEOUT_SECS),
+      /timed out/,
+      "The notification should never display."
+    );
+
+    ALERT_SERVICE.manualDoNotDisturb = false;
+  });
+});
+
+/**
+ * Test that the suppressForScreenSharing attribute can prevent
+ * notifications from appearing.
+ */
+add_task(async function test_suppressForScreenSharing() {
+  try {
+    // Only run the test if the do-not-disturb
+    // interface has been implemented.
+    ALERT_SERVICE.suppressForScreenSharing;
+    ok(true, "Alert service implements do-not-disturb interface");
+  } catch (e) {
+    ok(
+      true,
+      "Alert service doesn't implement do-not-disturb interface, exiting test"
+    );
+    return;
+  }
+
+  // In the event that something goes wrong during this test, make sure
+  // we put the attribute back to the default setting when this test file
+  // exits.
+  registerCleanupFunction(() => {
+    ALERT_SERVICE.suppressForScreenSharing = false;
+  });
+
+  // Make sure that do-not-disturb is not enabled before we start.
+  ok(
+    !ALERT_SERVICE.suppressForScreenSharing,
+    "Alert service should not be suppressing for screen sharing when test " +
+      "starts"
+  );
+
+  await BrowserTestUtils.withNewTab(PAGE, async browser => {
+    await openNotification(browser, "showNotification2");
+
+    info("Notification alert showing");
+    await closeNotification(browser);
+    ALERT_SERVICE.suppressForScreenSharing = true;
+
+    // The notification should not appear, but there is no way from the
+    // client-side to know that it was blocked, except for waiting some time
+    // and realizing that the "onshow" event never fired.
+    await Assert.rejects(
+      openNotification(browser, "showNotification2", NOTIFICATION_TIMEOUT_SECS),
+      /timed out/,
+      "The notification should never display."
+    );
+  });
+
+  ALERT_SERVICE.suppressForScreenSharing = false;
+});
--- a/src/zen/tests/mochitests/alerts/browser_notification_open_settings.js
+++ b/src/zen/tests/mochitests/alerts/browser_notification_open_settings.js
@@ -0,0 +1,87 @@
+"use strict";
+
+var notificationURL =
+  "https://example.org/browser/browser/base/content/test/alerts/file_dom_notifications.html";
+// BrowserGlue passes "privacy-permissions" to openPreferences when the
+// notifications-open-settings observer fires; the Settings Redesign
+// LegacyPaneMappings shim routes that to the permissionsData pane.
+var expectedURL = Services.prefs.getBoolPref(
+  "browser.settings-redesign.enabled",
+  false
+)
+  ? "about:preferences#permissionsData"
+  : "about:preferences#privacy";
+
+add_task(async function test_settingsOpen_observer() {
+  info(
+    "Opening a dummy tab so openPreferences=>switchToTabHavingURI doesn't use the blank tab."
+  );
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:robots",
+    },
+    async function dummyTabTask() {
+      // Ensure preferences is loaded before removing the tab.
+      let syncPaneLoadedPromise = TestUtils.topicObserved(
+        "sync-pane-loaded",
+        () => true
+      );
+      let tabPromise = BrowserTestUtils.waitForNewTab(gBrowser, expectedURL);
+      info("simulate a notifications-open-settings notification");
+      let uri = NetUtil.newURI("https://example.com");
+      let principal = Services.scriptSecurityManager.createContentPrincipal(
+        uri,
+        {}
+      );
+      Services.obs.notifyObservers(principal, "notifications-open-settings");
+      let tab = await tabPromise;
+      ok(tab, "The notification settings tab opened");
+      await syncPaneLoadedPromise;
+      BrowserTestUtils.removeTab(tab);
+    }
+  );
+});
+
+add_task(async function test_settingsOpen_button() {
+  info("Adding notification permission");
+  await addNotificationPermission(notificationURL);
+
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: notificationURL,
+    },
+    async function tabTask(aBrowser) {
+      info("Waiting for notification");
+      await openNotification(aBrowser, "showNotification2");
+
+      let alertWindow = Services.wm.getMostRecentWindow("alert:alert");
+      if (!alertWindow) {
+        ok(true, "Notifications don't use XUL windows on all platforms.");
+        await closeNotification(aBrowser);
+        return;
+      }
+
+      // Ensure preferences is loaded before removing the tab.
+      let syncPaneLoadedPromise = TestUtils.topicObserved(
+        "sync-pane-loaded",
+        () => true
+      );
+      let closePromise = promiseWindowClosed(alertWindow);
+      let tabPromise = BrowserTestUtils.waitForNewTab(gBrowser, expectedURL);
+      let openSettingsMenuItem = alertWindow.document.getElementById(
+        "openSettingsMenuItem"
+      );
+      openSettingsMenuItem.click();
+
+      info("Waiting for notification settings tab");
+      let tab = await tabPromise;
+      ok(tab, "The notification settings tab opened");
+
+      await syncPaneLoadedPromise;
+      await closePromise;
+      BrowserTestUtils.removeTab(tab);
+    }
+  );
+});
--- a/src/zen/tests/mochitests/alerts/browser_notification_remove_permission.js
+++ b/src/zen/tests/mochitests/alerts/browser_notification_remove_permission.js
@@ -0,0 +1,85 @@
+"use strict";
+
+const { PermissionTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/PermissionTestUtils.sys.mjs"
+);
+
+var tab;
+var notificationURL =
+  "https://example.org/browser/browser/base/content/test/alerts/file_dom_notifications.html";
+var alertWindowClosed = false;
+var permRemoved = false;
+
+function test() {
+  waitForExplicitFinish();
+
+  registerCleanupFunction(function () {
+    gBrowser.removeTab(tab);
+    window.restore();
+  });
+
+  addNotificationPermission(notificationURL).then(function openTab() {
+    tab = BrowserTestUtils.addTab(gBrowser, notificationURL);
+    gBrowser.selectedTab = tab;
+    BrowserTestUtils.browserLoaded(tab.linkedBrowser).then(() => onLoad());
+  });
+}
+
+function onLoad() {
+  openNotification(tab.linkedBrowser, "showNotification2").then(onAlertShowing);
+}
+
+function onAlertShowing() {
+  info("Notification alert showing");
+
+  let alertWindow = Services.wm.getMostRecentWindow("alert:alert");
+  if (!alertWindow) {
+    ok(true, "Notifications don't use XUL windows on all platforms.");
+    closeNotification(tab.linkedBrowser).then(finish);
+    return;
+  }
+  ok(
+    PermissionTestUtils.testExactPermission(
+      notificationURL,
+      "desktop-notification"
+    ),
+    "Permission should exist prior to removal"
+  );
+  let disableForOriginMenuItem = alertWindow.document.getElementById(
+    "disableForOriginMenuItem"
+  );
+  is(disableForOriginMenuItem.localName, "menuitem", "menuitem found");
+  Services.obs.addObserver(permObserver, "perm-changed");
+  alertWindow.addEventListener("beforeunload", onAlertClosing);
+  disableForOriginMenuItem.click();
+  info("Clicked on disable-for-origin menuitem");
+}
+
+function permObserver(subject, topic, data) {
+  if (topic != "perm-changed") {
+    return;
+  }
+
+  let permission = subject.QueryInterface(Ci.nsIPermission);
+  is(
+    permission.type,
+    "desktop-notification",
+    "desktop-notification permission changed"
+  );
+  is(data, "deleted", "desktop-notification permission deleted");
+
+  Services.obs.removeObserver(permObserver, "perm-changed");
+  permRemoved = true;
+  if (alertWindowClosed) {
+    finish();
+  }
+}
+
+function onAlertClosing(event) {
+  event.target.removeEventListener("beforeunload", onAlertClosing);
+
+  alertWindowClosed = true;
+  if (permRemoved) {
+    finish();
+  }
+}
--- a/src/zen/tests/mochitests/alerts/browser_notification_tab_switching.js
+++ b/src/zen/tests/mochitests/alerts/browser_notification_tab_switching.js
@@ -0,0 +1,116 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+"use strict";
+
+const { PermissionTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/PermissionTestUtils.sys.mjs"
+);
+
+var tab;
+var notification;
+var notificationURL =
+  "https://example.org/browser/browser/base/content/test/alerts/file_dom_notifications.html";
+var newWindowOpenedFromTab;
+
+add_task(async function test_notificationPreventDefaultAndSwitchTabs() {
+  await addNotificationPermission(notificationURL);
+
+  let originalTab = gBrowser.selectedTab;
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: notificationURL,
+    },
+    async function dummyTabTask(aBrowser) {
+      // Put new tab in background so it is obvious when it is re-focused.
+      await BrowserTestUtils.switchTab(gBrowser, originalTab);
+      isnot(
+        gBrowser.selectedBrowser,
+        aBrowser,
+        "Notification page loaded as a background tab"
+      );
+
+      // First, show a notification that will be have the tab-switching prevented.
+      function promiseNotificationEvent(evt) {
+        return SpecialPowers.spawn(
+          aBrowser,
+          [evt],
+          async function (contentEvt) {
+            return new Promise(resolve => {
+              let contentNotification = content.wrappedJSObject._notification;
+              contentNotification.addEventListener(
+                contentEvt,
+                function (event) {
+                  resolve({ defaultPrevented: event.defaultPrevented });
+                },
+                { once: true }
+              );
+            });
+          }
+        );
+      }
+      await openNotification(aBrowser, "showNotification1");
+      info("Notification alert showing");
+      let alertWindow = Services.wm.getMostRecentWindow("alert:alert");
+      if (!alertWindow) {
+        ok(true, "Notifications don't use XUL windows on all platforms.");
+        await closeNotification(aBrowser);
+        return;
+      }
+      info("Clicking on notification");
+      let promiseClickEvent = promiseNotificationEvent("click");
+
+      // NB: This executeSoon is needed to allow the non-e10s runs of this test
+      // a chance to set the event listener on the page. Otherwise, we
+      // synchronously fire the click event before we listen for the event.
+      executeSoon(() => {
+        EventUtils.synthesizeMouseAtCenter(
+          alertWindow.document.getElementById("alertTitleLabel"),
+          {},
+          alertWindow
+        );
+      });
+      let clickEvent = await promiseClickEvent;
+      ok(
+        clickEvent.defaultPrevented,
+        "The event handler for the first notification cancels the event"
+      );
+      isnot(
+        gBrowser.selectedBrowser,
+        aBrowser,
+        "Notification page still a background tab"
+      );
+      let notificationClosed = promiseNotificationEvent("close");
+      await closeNotification(aBrowser);
+      await notificationClosed;
+
+      // Second, show a notification that will cause the tab to get switched.
+      await openNotification(aBrowser, "showNotification2");
+      alertWindow = Services.wm.getMostRecentWindow("alert:alert");
+      let promiseTabSelect = BrowserTestUtils.waitForEvent(
+        gBrowser.tabContainer,
+        "TabSelect"
+      );
+      EventUtils.synthesizeMouseAtCenter(
+        alertWindow.document.getElementById("alertTitleLabel"),
+        {},
+        alertWindow
+      );
+      await promiseTabSelect;
+      is(
+        gBrowser.selectedBrowser.currentURI.spec,
+        notificationURL,
+        "Clicking on the second notification should select its originating tab"
+      );
+      notificationClosed = promiseNotificationEvent("close");
+      await closeNotification(aBrowser);
+      await notificationClosed;
+    }
+  );
+});
+
+add_task(async function cleanup() {
+  PermissionTestUtils.remove(notificationURL, "desktop-notification");
+});
--- a/src/zen/tests/mochitests/alerts/file_dom_notifications.html
+++ b/src/zen/tests/mochitests/alerts/file_dom_notifications.html
@@ -0,0 +1,39 @@
+<html>
+<head>
+<meta charset="utf-8">
+<script>
+"use strict";
+
+function showNotification1() {
+  var options = {
+      dir: undefined,
+      lang: undefined,
+      body: "Test body 1",
+      tag: "Test tag",
+      icon: undefined,
+  };
+  var n = new Notification("Test title", options);
+  n.addEventListener("click", function(event) {
+    event.preventDefault();
+  });
+  return n;
+}
+
+function showNotification2() {
+  var options = {
+      dir: undefined,
+      lang: undefined,
+      body: "Test body 2",
+      tag: "Test tag",
+      icon: undefined,
+  };
+  return new Notification("Test title", options);
+}
+</script>
+</head>
+<body>
+<form id="notificationForm" onsubmit="showNotification();">
+  <input type="submit" value="Show notification" id="submit"/>
+</form>
+</body>
+</html>
--- a/src/zen/tests/mochitests/alerts/head.js
+++ b/src/zen/tests/mochitests/alerts/head.js
@@ -0,0 +1,73 @@
+// Platforms may default to reducing motion. We override this to ensure the
+// alert slide animation is enabled in tests.
+SpecialPowers.pushPrefEnv({
+  set: [["ui.prefersReducedMotion", 0]],
+});
+
+async function addNotificationPermission(originString) {
+  return SpecialPowers.pushPermissions([
+    {
+      type: "desktop-notification",
+      allow: true,
+      context: originString,
+    },
+  ]);
+}
+
+/**
+ * Similar to `BrowserTestUtils.closeWindow`, but
+ * doesn't call `window.close()`.
+ */
+function promiseWindowClosed(window) {
+  return new Promise(function (resolve) {
+    Services.ww.registerNotification(function observer(subject, topic) {
+      if (topic == "domwindowclosed" && subject == window) {
+        Services.ww.unregisterNotification(observer);
+        resolve();
+      }
+    });
+  });
+}
+
+/**
+ * These two functions work with file_dom_notifications.html to open the
+ * notification and close it.
+ *
+ * |fn| can be showNotification1 or showNotification2.
+ * if |timeout| is passed, then the promise returned from this function is
+ * rejected after the requested number of miliseconds.
+ */
+function openNotification(aBrowser, fn, timeout) {
+  info(`openNotification: ${fn}`);
+  return SpecialPowers.spawn(
+    aBrowser,
+    [fn, timeout],
+    async function (contentFn, contentTimeout) {
+      await new Promise((resolve, reject) => {
+        let win = content.wrappedJSObject;
+        let notification = win[contentFn]();
+        win._notification = notification;
+
+        function listener() {
+          notification.removeEventListener("show", listener);
+          resolve();
+        }
+
+        notification.addEventListener("show", listener);
+
+        if (contentTimeout) {
+          content.setTimeout(() => {
+            notification.removeEventListener("show", listener);
+            reject("timed out");
+          }, contentTimeout);
+        }
+      });
+    }
+  );
+}
+
+function closeNotification(aBrowser) {
+  return SpecialPowers.spawn(aBrowser, [], function () {
+    content.wrappedJSObject._notification.close();
+  });
+}
--- a/src/zen/tests/mochitests/backforward/browser.toml
+++ b/src/zen/tests/mochitests/backforward/browser.toml
@@ -0,0 +1,7 @@
+[DEFAULT]
+
+["browser_history_menu.js"]
+fail-if = [
+  "a11y_checks", # Bug 1854233 navigator-toolbox may not be focusable
+]
+https_first_disabled = true
--- a/src/zen/tests/mochitests/backforward/browser_history_menu.js
+++ b/src/zen/tests/mochitests/backforward/browser_history_menu.js
@@ -0,0 +1,179 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// This test verifies that the back forward button long-press menu and context menu
+// shows the correct history items.
+
+add_task(async function mousedown_back() {
+  await testBackForwardMenu(false);
+});
+
+add_task(async function contextmenu_back() {
+  await testBackForwardMenu(true);
+});
+
+async function openHistoryMenu(useContextMenu) {
+  let backButton = document.getElementById("back-button");
+  let rect = backButton.getBoundingClientRect();
+
+  info("waiting for the history menu to open");
+
+  let popupShownPromise = BrowserTestUtils.waitForEvent(
+    useContextMenu ? document.getElementById("backForwardMenu") : backButton,
+    "popupshown"
+  );
+  if (useContextMenu) {
+    EventUtils.synthesizeMouseAtCenter(backButton, {
+      type: "contextmenu",
+      button: 2,
+    });
+  } else {
+    EventUtils.synthesizeMouseAtCenter(backButton, { type: "mousedown" });
+  }
+
+  EventUtils.synthesizeMouse(backButton, rect.width / 2, rect.height, {
+    type: "mouseup",
+  });
+  let popupEvent = await popupShownPromise;
+
+  ok(true, "history menu opened");
+
+  return popupEvent;
+}
+
+async function testBackForwardMenu(useContextMenu) {
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+    "http://example.com"
+  );
+
+  for (let iter = 2; iter <= 4; iter++) {
+    // Iterate three times. For the first two times through the loop, add a new history item.
+    // But for the last iteration, go back in the history instead.
+    await SpecialPowers.spawn(
+      gBrowser.selectedBrowser,
+      [iter],
+      async function (iterChild) {
+        if (iterChild == 4) {
+          let popStatePromise = new Promise(function (resolve) {
+            content.onpopstate = resolve;
+          });
+          content.history.back();
+          await popStatePromise;
+        } else {
+          // With the back-button intervention enabled, we need to make sure to
+          // trigger a user activation on each history entry, or they won't
+          // show in the menu.
+          content.document.notifyUserGestureActivation();
+          content.history.pushState({}, "" + iterChild, iterChild + ".html");
+        }
+      }
+    );
+
+    // Wait for the session data to be flushed before continuing the test
+    await new Promise(resolve =>
+      SessionStore.getSessionHistory(gBrowser.selectedTab, resolve)
+    );
+
+    let popupEvent = await openHistoryMenu(useContextMenu);
+
+    // Wait for the session data to be flushed before continuing the test
+    await new Promise(resolve =>
+      SessionStore.getSessionHistory(gBrowser.selectedTab, resolve)
+    );
+
+    is(
+      popupEvent.target.children.length,
+      iter > 3 ? 3 : iter,
+      "Correct number of history items"
+    );
+
+    let node = popupEvent.target.lastElementChild;
+    // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+    is(node.getAttribute("uri"), "http://example.com/", "'1' item uri");
+    is(node.getAttribute("index"), "0", "'1' item index");
+    is(
+      node.getAttribute("historyindex"),
+      iter == 3 ? "-2" : "-1",
+      "'1' item historyindex"
+    );
+
+    node = node.previousElementSibling;
+    // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+    is(node.getAttribute("uri"), "http://example.com/2.html", "'2' item uri");
+    is(node.getAttribute("index"), "1", "'2' item index");
+    is(
+      node.getAttribute("historyindex"),
+      iter == 3 ? "-1" : "0",
+      "'2' item historyindex"
+    );
+
+    if (iter >= 3) {
+      node = node.previousElementSibling;
+      // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+      is(node.getAttribute("uri"), "http://example.com/3.html", "'3' item uri");
+      is(node.getAttribute("index"), "2", "'3' item index");
+      is(
+        node.getAttribute("historyindex"),
+        iter == 4 ? "1" : "0",
+        "'3' item historyindex"
+      );
+    }
+
+    // Close the popup, but on the last iteration, click on one of the history items
+    // to ensure it opens in a new tab.
+    let popupHiddenPromise = BrowserTestUtils.waitForEvent(
+      popupEvent.target,
+      "popuphidden"
+    );
+
+    if (iter < 4) {
+      popupEvent.target.hidePopup();
+    } else {
+      let newTabPromise = BrowserTestUtils.waitForNewTab(
+        gBrowser,
+        // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+        url => url == "http://example.com/"
+      );
+
+      popupEvent.target.activateItem(popupEvent.target.children[2], {
+        button: 1,
+      });
+
+      let newtab = await newTabPromise;
+      gBrowser.removeTab(newtab);
+    }
+
+    await popupHiddenPromise;
+  }
+
+  gBrowser.removeTab(tab);
+}
+
+// Make sure that the history popup appears after navigating around in a preferences page.
+add_task(async function test_preferences_page() {
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    "about:preferences"
+  );
+
+  openPreferences("search");
+  let popupEvent = await openHistoryMenu(true);
+
+  // Wait for the session data to be flushed before continuing the test
+  await new Promise(resolve =>
+    SessionStore.getSessionHistory(gBrowser.selectedTab, resolve)
+  );
+
+  is(popupEvent.target.children.length, 2, "Correct number of history items");
+
+  let popupHiddenPromise = BrowserTestUtils.waitForEvent(
+    popupEvent.target,
+    "popuphidden"
+  );
+  popupEvent.target.hidePopup();
+  await popupHiddenPromise;
+
+  gBrowser.removeTab(tab);
+});
--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
mr. m	e89bd7796e	gh-15154: Fixed stale containers trying to sync across devices (gh-15166)	2026-08-30 00:42:45 +02:00
mr. m	66c5931a29	gh-15163: Sync upstream Firefox to version `155.0` RC (gh-15164)	2026-08-30 00:26:45 +02:00
Fernando Omori	a5585c5619	gh-14380: Fix sidebar width getting stuck when toggling layout on the right side (gh-15092)	2026-08-29 12:35:31 +02:00
mr. m	2326d2b56b	gh-15157: Add support for squircles on the Chrome UI (gh-14009)	2026-08-29 12:35:17 +02:00
mr. m	9ef1d96c00	Revert "gh-15144: Update windows registry on update" (gh-15153)	2026-08-29 01:34:29 +02:00
Nikola Hristov	432f93770f	gh-15146: Fix bad current view index after removing a group (gh-15147)	2026-08-28 19:58:05 +02:00
mr. m	f28e0688fb	gh-15144: Update windows registry on update (gh-15145)	2026-08-28 11:55:40 +02:00
Nikola Hristov	8df6fef1ac	gh-15115: Tests for urlbar close and split view (gh-15118) Co-authored-by: mr. m <91018726+mr-cheffy@users.noreply.github.com>	2026-08-27 23:45:37 +02:00
mr. m	4746d36699	gh-15088: Prevent sync if engine is already applying (gh-15137)	2026-08-27 23:38:47 +02:00
Nikola Hristov	9e0c790602	gh-15134: Fixes tab removed from group getting focused (gh-15135) Closes https://github.com/zen-browser/desktop/issues/15134 Fix video: https://github.com/user-attachments/assets/1c06ea7f-d482-4d4a-8bbe-df41daa27616	2026-08-27 22:40:43 +02:00
mr. m	3d53b37e8b	gh-15119: Update windows registry with old certificates (gh-15120)	2026-08-26 17:51:09 +02:00
Nikola Hristov	e7ddfb52db	gh-15115: Fix creating empty split view with url bar open (gh-15116)	2026-08-26 13:16:13 +02:00
mr. m	ba70449bdd	gh-15088: Add debug log for space sync (gh-15117)	2026-08-26 12:23:52 +02:00
mr. m	bf40c31149	gh-14710: Fixed minimizing PiP window failing to collapse into the sidebar (gh-15111)	2026-08-26 08:30:00 +02:00
mr. m	7a093beae4	gh-15084: Fixed incoming tab icons applying to active tabs (gh-15107)	2026-08-25 22:31:50 +02:00
mr. m	03b4e934fe	gh-15091: Fixed race condition when syncing new space and container (gh-15106)	2026-08-25 22:21:19 +02:00
mr. m	b93d19b873	gh-15088: Fixed syncing essentials with different containers (gh-15105)	2026-08-25 22:05:54 +02:00
mr. m	b9c4000fe2	gh-15101: Sync upstream Firefox to version `154.0.1` (gh-15100)	2026-08-25 19:37:07 +02:00
mr. m	0b7687ec6d	gh-14990: Prevent policyContainer from bloating the session file (gh-15098)	2026-08-25 13:41:10 +02:00
mr. m	d70b3d902c	gh-15085: Import mochitests for remote settings (gh-15086)	2026-08-24 22:52:33 +02:00
mr. m	f9f8f2f372	gh-15075: Fixed syncing new tabs not using static labels (gh-15079) Fixes https://github.com/zen-browser/desktop/issues/15075	2026-08-24 18:27:50 +02:00
mr. m	99dca42723	gh-14470: Prevent state override if url changed (gh-15070)	2026-08-23 16:40:30 +02:00
Henrik Nyh	ed0a6fd447	gh-15039: Use Title Case for split view labels (gh-15059)	2026-08-23 12:21:34 +02:00
CocoLng	88c6611f1e	gh-15039: Fix New Blank Window menu entry not in Title Case (gh-15056)	2026-08-22 10:08:37 +02:00
mr. m	e66e763e63	gh-14470: Fixed wrong data image being used for sync (gh-15048)	2026-08-21 09:44:49 +02:00
mr. m	721135f576	gh-14470: Fixed moz-remote-urls not being synced correctly (gh-15043)	2026-08-21 01:24:25 +02:00
mr. m	d8a934d2ec	gh-15029: Fixed urlbar suggestion context not working (gh-15037)	2026-08-20 21:57:35 +02:00
mr. m	91a1d4d2ca	gh-14470: Run sweep animation on first sync (gh-15036)	2026-08-20 21:38:09 +02:00
mr. m	97577dac26	gh-15031: Fixed duplicate separator on tab context menu (gh-15035)	2026-08-20 21:18:13 +02:00
Kristijan Ribarić	5723a89bcd	gh-14470: Add tab and folder sync support (gh-13984) Co-authored-by: mr. m <91018726+mr-cheffy@users.noreply.github.com>	2026-08-20 19:16:13 +02:00