diff --git a/browser/components/tabbrowser/Tabbrowser.sys.mjs b/browser/components/tabbrowser/Tabbrowser.sys.mjs
index f68e37926001384d0c8e80a3c163dc89e9c4ee5c..350cebd50aa6ee58fbbbb53d0f5334aa074f1ac2 100644
--- a/browser/components/tabbrowser/Tabbrowser.sys.mjs
+++ b/browser/components/tabbrowser/Tabbrowser.sys.mjs
@@ -484,6 +484,7 @@ export class Tabbrowser {
    * @type {MozBrowser[]}
    */
   get splitViewBrowsers() {
+    return this.documentGlobal.gZenViewSplitter.splitViewBrowsers;
     const browsers = [];
     if (this.#activeSplitView) {
       for (const tab of this.#activeSplitView.tabs) {
@@ -582,15 +583,74 @@ export class Tabbrowser {
     return this.tabContainer.visibleTabs;
   }
 
+  zenHandleTabMove(...args) {
+    return this.#handleTabMove(...args);
+  }
+
+  get zenTabProgressListener() { return TabProgressListener; }
+
+  get TabStateFlusher() {
+    return lazy.TabStateFlusher;
+  }
+
+  get AsyncTabSwitcher() {
+    return lazy.AsyncTabSwitcher;
+  }
+
+  get _numVisiblePinTabsWithoutCollapsed() {
+    let i = 0;
+    for (let item of this.tabContainer.ariaFocusableItems) {
+      if (this.isTabGroupLabel(item) && item.group?.pinned) {
+        i += 1;
+        continue;
+      }
+      if (!item.pinned && !item.hasAttribute("zen-glance-tab")) {
+        break;
+      }
+      if (item.visible) {
+        i += !item.hasAttribute("zen-glance-tab");
+      }
+    }
+    return i;
+  }
+
+  ungroupTabsUntilNoActive(tab) {
+    if (!tab || !tab.group) return;
+    const activeGroups = tab.group.activeGroups;
+    if (activeGroups?.length) {
+      const lastActiveGroup = activeGroups[activeGroups.length - 1];
+      this.#handleTabMove(tab, () => {
+        lastActiveGroup.after(tab);
+      });
+    }
+  }
+
+  get _numZenEssentials() {
+    let i = 0;
+    for (let tab of this.tabs) {
+      if (!tab.hasAttribute("zen-essential") && !tab.hasAttribute("zen-glance-tab")) {
+        break;
+      }
+      i += !tab.hasAttribute("zen-glance-tab");
+    }
+    return i;
+  }
+
   get pinnedTabCount() {
-    for (var i = 0; i < this.tabs.length; i++) {
-      if (!this.tabs[i].pinned) {
+    let i = 0;
+    for (let tab of this.tabs) {
+      if (!tab.pinned && !tab.hasAttribute("zen-glance-tab")) {
         break;
       }
+      i += !tab.hasAttribute("zen-glance-tab");
     }
     return i;
   }
 
+  get tabsWithoutGlance() {
+    return this.tabs.filter(tab => !tab.hasAttribute("zen-glance-tab"));
+  }
+
   setSelectedTab(val, metricsContext = null) {
     if (this.selectedTab === val) {
       return;
@@ -603,6 +663,9 @@ export class Tabbrowser {
     ) {
       return;
     }
+    if (this.documentGlobal.gZenWorkspaces.onBeforeTabSelect(val)) {
+      return;
+    }
     // Update the tab
     this.tabbox.selectedTab = val;
 
@@ -688,6 +751,10 @@ export class Tabbrowser {
       userContextId = parseInt(tabArgument.getAttribute("usercontextid"), 10);
     }
 
+    if (typeof this.documentGlobal._zenStartupUnsyncedUserContextId == 'number') {
+      userContextId = this.documentGlobal._zenStartupUnsyncedUserContextId;
+    }
+
     if (openWindowInfo) {
       userContextId = openWindowInfo.originAttributes.userContextId;
     }
@@ -786,6 +853,8 @@ export class Tabbrowser {
     this.tabpanels.appendChild(panel);
 
     let tab = this.tabs[0];
+    this.documentGlobal.gZenWorkspaces.handleInitialTab(tab, (!remoteType || remoteType === lazy.E10SUtils.PRIVILEGEDABOUT_REMOTE_TYPE) && !this.documentGlobal.gZenUIManager.testingEnabled);
+    tab._zenContentsVisible = true;
     tab.linkedPanel = uniqueId;
     this.#selectedTab = tab;
     this.#selectedBrowser = browser;
@@ -1234,18 +1303,24 @@ export class Tabbrowser {
    *   The context for the operation for telemetry purposes, defaults to an unknown context.
    */
   pinTab(aTab, { metricsContext = this.TabMetrics.UNKNOWN_CONTEXT } = {}) {
+    aTab = this.documentGlobal.gZenGlanceManager.getTabOrGlanceParent(aTab);
     if (aTab.pinned || aTab == this.documentGlobal.FirefoxViewHandler.tab) {
       return;
     }
 
     this.showTab(aTab);
+    const handled = this.documentGlobal.gZenFolders.handleTabPin(aTab);
+    if (!handled) {
+      this.ungroupTab(aTab);
     this.#handleTabMove(aTab, () => {
       let periphery = this.document.getElementById(
         "pinned-tabs-container-periphery"
       );
       // If periphery is null, append to end
-      this.pinnedTabsContainer.insertBefore(aTab, periphery);
+      this.tabContainer.tabDragAndDrop.handle_drop_transition(this.tabs[this.pinnedTabCount - 1], aTab, [aTab], false);
+      aTab.hasAttribute("zen-essential") ? this.documentGlobal.gZenWorkspaces.getEssentialsSection(aTab).appendChild(aTab) : this.pinnedTabsContainer.insertBefore(aTab, this.pinnedTabsContainer.lastChild)
     });
+    }
 
     aTab.setAttribute("pinned", "true");
     this.#updateTabBarForPinnedTabs();
@@ -1262,16 +1337,25 @@ export class Tabbrowser {
    *   The context for the operation for telemetry purposes, defaults to an unknown context.
    */
   unpinTab(aTab, { metricsContext = this.TabMetrics.UNKNOWN_CONTEXT } = {}) {
+    aTab = this.documentGlobal.gZenGlanceManager.getTabOrGlanceParent(aTab);
     if (!aTab.pinned) {
       return;
     }
 
     this.#handleTabMove(aTab, () => {
+      const handled = this.documentGlobal.gZenFolders.handleTabUnpin(aTab);
+      if (!handled) {
+        this.tabContainer.tabDragAndDrop.handle_drop_transition(this.tabs[this.pinnedTabCount + 1 /* empty + extra */], aTab, [aTab], true);
+      }
+
       // we remove this attribute first, so that allTabs represents
       // the moving of a tab from the pinned tabs container
       // and back into arrowscrollbox.
       aTab.removeAttribute("pinned");
-      this.tabContainer.arrowScrollbox.prepend(aTab);
+      aTab.removeAttribute("zen-essential");
+      if (!handled) {
+        this.documentGlobal.gZenWorkspaces.activeWorkspaceStrip.prepend(aTab);
+      }
     });
 
     aTab.style.marginInlineStart = "";
@@ -1494,6 +1578,9 @@ export class Tabbrowser {
 
     let LOCAL_PROTOCOLS = ["chrome:", "about:", "resource:", "data:"];
 
+    try {
+      aIconURL = aTab.zenStaticIcon || aIconURL;
+      this.documentGlobal.gZenPinnedTabManager.onTabIconChanged(aTab, aIconURL);
     if (
       aIconURL &&
       !LOCAL_PROTOCOLS.some(protocol => aIconURL.startsWith(protocol))
@@ -1503,6 +1590,9 @@ export class Tabbrowser {
       );
       return;
     }
+    } catch (e) {
+      console.warn(e);
+    }
 
     let browser = this.getBrowserForTab(aTab);
     browser.mIconURL = aIconURL;
@@ -1831,7 +1921,6 @@ export class Tabbrowser {
 
     // Preview mode should not reset the owner
     if (!this.#previewMode && !oldTab.selected) {
-      oldTab.owner = null;
     }
 
     let lastRelatedTab = this.#lastRelatedTabMap.get(oldTab);
@@ -1922,6 +2011,7 @@ export class Tabbrowser {
     if (!this.#previewMode) {
       newTab.recordTimeFromUnloadToReload();
       newTab.updateLastAccessed();
+      newTab.removeAttribute("unread");
       oldTab.updateLastAccessed();
       // if this is the foreground window, update the last-seen timestamps.
       if (this.documentGlobal == lazy.BrowserWindowTracker.getTopWindow()) {
@@ -2136,6 +2226,9 @@ export class Tabbrowser {
     }
 
     let activeEl = this.document.activeElement;
+    if (this.documentGlobal.gURLBar._zenHandleUrlbarClose) {
+      this.documentGlobal.gURLBar._zenHandleUrlbarClose(true);
+    }
     // If focus is on the old tab, move it to the new tab.
     if (activeEl == oldTab) {
       newTab.focus();
@@ -2174,7 +2267,7 @@ export class Tabbrowser {
     // 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.
-    if (this.documentGlobal.gURLBar.getBrowserState(newBrowser).urlbarFocused) {
+    if (this.documentGlobal.gURLBar.getBrowserState(newBrowser).urlbarFocused && (!this.documentGlobal.gZenVerticalTabsManager._hasSetSingleToolbar || this.documentGlobal.isBlankPageURL(newBrowser.currentURI?.spec))) {
       let selectURL = () => {
         if (this.#asyncTabSwitching) {
           // Set _awaitingSetURI flag to suppress popup notification
@@ -2478,6 +2571,10 @@ export class Tabbrowser {
     return this.#setTabLabel(aTab, aLabel);
   }
 
+  _setTabLabel(aTab, aLabel, aOptions) {
+    return this.#setTabLabel(aTab, aLabel, aOptions);
+  }
+
   /**
    * Sets a tab's label, shortened and clamped for display.
    *
@@ -2498,7 +2595,12 @@ export class Tabbrowser {
    * @returns {boolean}
    *   Whether the label changed.
    */
-  #setTabLabel(aTab, aLabel, { beforeTabOpen, isContentTitle, isURL } = {}) {
+  #setTabLabel(aTab, aLabel, { beforeTabOpen, isContentTitle, isURL, _zenChangeLabelFlag } = {}) {
+    if (!aTab._zenContentsVisible && !aTab._zenChangeLabelFlag && !aTab._labelIsInitialTitle && !this.documentGlobal.gZenWorkspaces.privateWindowOrDisabled && !_zenChangeLabelFlag) {
+      return false;
+    }
+    aLabel = (typeof aTab.zenStaticLabel === "string" && aTab.zenStaticLabel) ? aTab.zenStaticLabel : aLabel;
+    this.documentGlobal.gZenPinnedTabManager.onTabLabelChanged(aTab);
     if (!aLabel || (isURL && /^about:reader\?url=/.test(aLabel))) {
       return false;
     }
@@ -2657,7 +2759,7 @@ export class Tabbrowser {
       newIndex = this.selectedTab.index + 1;
     }
 
-    if (replace) {
+    if (replace && !((targetTab || this.selectedTab)?.hasAttribute('zen-empty-tab'))) {
       if (this.isTabGroupLabel(targetTab)) {
         throw new Error(
           "Replacing a tab group label with a tab is not supported"
@@ -2971,6 +3073,7 @@ export class Tabbrowser {
     uriIsAboutBlank,
     userContextId,
     skipLoad,
+    _forZenEmptyTab,
   } = {}) {
     let b = this.document.createXULElement("browser");
     // Use the JSM global to create the permanentKey, so that if the
@@ -3045,10 +3148,7 @@ export class Tabbrowser {
       b.setAttribute("name", name);
     }
 
-    if (
-      lazy.AIWindow.isAIWindowActive(this.documentGlobal) ||
-      lazy.allowTransparentBrowser
-    ) {
+    if (lazy.allowTransparentBrowser || _forZenEmptyTab) {
       b.setAttribute("transparent", "true");
     }
 
@@ -3212,7 +3312,7 @@ export class Tabbrowser {
 
     let panel = this.getPanel(browser);
     let uniqueId = this.#generateUniquePanelID();
-    panel.id = uniqueId;
+    if (!panel.id?.startsWith("zen-")) panel.id = uniqueId;
     aTab.linkedPanel = uniqueId;
 
     // Inject the <browser> into the DOM if necessary.
@@ -3269,8 +3369,8 @@ export class Tabbrowser {
     // 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) {
-      this.tabs[0].linkedBrowser.browsingContext.hasSiblings = true;
-      this.tabs[1].linkedBrowser.browsingContext.hasSiblings = true;
+      if (this.tabs[0].linkedBrowser.browsingContext) this.tabs[0].linkedBrowser.browsingContext.hasSiblings = true;
+      if (this.tabs[1].linkedBrowser.browsingContext) this.tabs[1].linkedBrowser.browsingContext.hasSiblings = true;
     } else {
       aTab.linkedBrowser.browsingContext.hasSiblings = this.tabs.length > 1;
     }
@@ -3458,7 +3558,6 @@ export class Tabbrowser {
             {
               tabIndex: tab.index + 1,
               userContextId: tab.userContextId,
-              tabGroup: tab.group,
               focusUrlBar: true,
             }
           );
@@ -3667,6 +3766,10 @@ export class Tabbrowser {
       schemelessInput,
       hasValidUserGestureActivation = false,
       textDirectiveUserActivation = false,
+      _forZenEmptyTab,
+      essential,
+      zenWorkspaceId,
+      skipRoute = false,
     } = {}
   ) {
     // all callers of addTab that pass a params object need to pass
@@ -3677,6 +3780,23 @@ export class Tabbrowser {
       );
     }
 
+    const beforeRouteResult = this.documentGlobal.gZenSpaceRoutingManager.onBeforeAddTab(uriString, { skipRoute, pinned, tabGroup, fromExternal }, this.documentGlobal);
+    if (beforeRouteResult.shouldEarlyExit) {
+      return null;
+    }
+
+    const originallyInBackground = inBackground;
+    inBackground ||= this.documentGlobal.gZenSpaceRoutingManager.shouldDeferTabSelection(beforeRouteResult, this.documentGlobal);
+
+    let hasZenDefaultUserContextId = false;
+    let zenForcedWorkspaceId = undefined;
+    if (beforeRouteResult.isRouteFound && (typeof userContextId === "undefined" || fromExternal)) {
+      userContextId = beforeRouteResult.userContextId;
+      hasZenDefaultUserContextId = true;
+    } else if (typeof this.documentGlobal.gZenWorkspaces !== "undefined" && !_forZenEmptyTab) {
+      [userContextId, hasZenDefaultUserContextId, zenForcedWorkspaceId] = this.documentGlobal.gZenWorkspaces.getContextIdIfNeeded(userContextId, fromExternal, triggeringPrincipal);
+    }
+
     if (!UserInteraction.running("browser.tabs.opening", this.documentGlobal)) {
       UserInteraction.start(
         "browser.tabs.opening",
@@ -3685,6 +3805,7 @@ export class Tabbrowser {
       );
     }
 
+    if (!this.documentGlobal.gURLBar.hasAttribute("zen-newtab")) {
     // If we're opening a foreground tab, set the owner by default.
     ownerTab ??= inBackground ? null : this.selectedTab;
 
@@ -3692,6 +3813,7 @@ export class Tabbrowser {
     if (this.selectedTab.owner) {
       this.selectedTab.owner = null;
     }
+    }
 
     // Find the tab that opened this one, if any. This is used for
     // determining positioning, and inherited attributes such as the
@@ -3744,6 +3866,22 @@ export class Tabbrowser {
         noInitialLabel,
         skipBackgroundNotify,
       });
+      if (hasZenDefaultUserContextId) {
+        t.setAttribute("zenDefaultUserContextId", "true");
+      }
+      if (zenWorkspaceId) {
+        t.setAttribute("zen-workspace-id", zenWorkspaceId);
+        t.setAttribute("change-workspace", "")
+      } else if (zenForcedWorkspaceId !== undefined) {
+        t.setAttribute("zen-workspace-id", zenForcedWorkspaceId);
+        t.setAttribute("change-workspace", "")
+      }
+      if (_forZenEmptyTab) {
+        t.setAttribute("zen-empty-tab", "true");
+      }
+      if (essential) {
+        t.setAttribute("zen-essential", "true");
+      }
       if (insertTab) {
         // Insert the tab into the tab container in the correct position.
         this.#insertTabAtIndex(t, {
@@ -3752,6 +3890,7 @@ export class Tabbrowser {
           ownerTab,
           openerTab,
           pinned,
+          essential,
           bulkOrderedOpen,
           tabGroup: tabGroup ?? openerTab?.group,
         });
@@ -3770,6 +3909,7 @@ export class Tabbrowser {
         openWindowInfo,
         skipLoad,
         triggeringRemoteType,
+        _forZenEmptyTab,
       }));
 
       if (focusUrlBar) {
@@ -3894,6 +4034,12 @@ export class Tabbrowser {
       }
     }
 
+    if (typeof this.documentGlobal.gZenVerticalTabsManager !== "undefined") {
+      this.documentGlobal.gZenVerticalTabsManager.animateItemOpen(t);
+    }
+    if (typeof this.documentGlobal.gZenCompactModeManager !== "undefined" && !skipLoad && insertTab) {
+      this.documentGlobal.gZenCompactModeManager._onTabOpen(t, originallyInBackground, beforeRouteResult);
+    }
     // Additionally send pinned tab events
     if (pinned) {
       this.#notifyPinnedStatus(t);
@@ -3904,6 +4050,15 @@ export class Tabbrowser {
     if (!inBackground) {
       this.selectedTab = t;
     }
+
+    this.documentGlobal.gZenSpaceRoutingManager.onAfterAddTab(
+      uriString,
+      t,
+      { skipRoute: skipRoute || _forZenEmptyTab, fromExternal, pinned, tabGroup, inBackground: originallyInBackground },
+      this.documentGlobal,
+      beforeRouteResult,
+    );
+
     return t;
   }
 
@@ -4125,6 +4280,7 @@ export class Tabbrowser {
       insertBefore = null,
       isAdoptingGroup = false,
       metricsContext = this.TabMetrics.UNKNOWN_CONTEXT,
+      forSplitView = false,
     } = {}
   ) {
     if (
@@ -4135,7 +4291,6 @@ export class Tabbrowser {
           !this.isSplitViewWrapper(tabOrSplitView)
       )
     ) {
-      throw new Error("Cannot create tab group with zero tabs or split views");
     }
 
     if (!color) {
@@ -4150,7 +4305,15 @@ export class Tabbrowser {
       id = `${Date.now()}-${Math.round(Math.random() * 100)}`;
     }
     let group = this.#createTabGroup(id, color, false, label, isAdoptingGroup);
-    this.tabContainer.insertBefore(group, insertBefore?.group ?? insertBefore);
+    if (forSplitView) {
+      group.setAttribute('split-view-group', true);
+    }
+    group.essential = tabsAndSplitViews.some(tab => tab.hasAttribute("essential"));
+    group.pinned = group.essential || tabsAndSplitViews.some(tab => tab.pinned);
+    if (forSplitView && !insertBefore?.group?.isZenFolder) insertBefore = insertBefore?.group ?? insertBefore;
+    insertBefore.before(
+      group,
+    );
     group.addTabs(tabsAndSplitViews, metricsContext);
 
     // Bail out if the group is empty at this point. This can happen if all
@@ -4253,7 +4416,7 @@ export class Tabbrowser {
     }
 
     this.#handleTabMove(tab, () =>
-      this.tabContainer.insertBefore(tab, tab.group.nextElementSibling)
+      tab.group.after(tab)
     );
   }
 
@@ -4337,6 +4500,7 @@ export class Tabbrowser {
       color: group.color,
       insertBefore: newTabs[0],
       isAdoptingGroup: true,
+      forSplitView: group.hasAttribute('split-view-group'),
     });
   }
 
@@ -4597,6 +4761,7 @@ export class Tabbrowser {
       openWindowInfo,
       skipLoad,
       triggeringRemoteType,
+      _forZenEmptyTab
     }
   ) {
     // If we don't have a preferred remote type (or it is `NOT_REMOTE`), and
@@ -4660,6 +4825,7 @@ export class Tabbrowser {
         openWindowInfo,
         name,
         skipLoad,
+        _forZenEmptyTab
       });
     }
 
@@ -4943,8 +5109,9 @@ export class Tabbrowser {
       }
 
       // Add a new tab if needed.
-      if (!tab) {
-        let createLazyBrowser = restoreTabsLazily && !select && !tabData.pinned;
+      if (!tab || tab?._markedForReplacement) {
+        let createLazyBrowser =
+          restoreTabsLazily && !(tabData.pinned && !Services.prefs.getBoolPref("browser.sessionstore.restore_pinned_tabs_on_demand"));
 
         let url = "about:blank";
         if (tabData.entries?.length) {
@@ -4977,8 +5144,10 @@ export class Tabbrowser {
           insertTab: false,
           skipLoad: true,
           preferredRemoteType,
+          _forZenEmptyTab: tabData.zenIsEmpty,
         });
-
+        tab._originalUrl = url;
+        this.documentGlobal.gZenSessionStore.restoreInitialTabData(tab, tabData);
         if (select) {
           tabToSelect = tab;
         }
@@ -5000,7 +5169,8 @@ export class Tabbrowser {
         this.pinTab(tab);
         // Then ensure all the tab open/pinning information is sent.
         this.#fireTabOpen(tab, {});
-      } else if (tabData.groupId) {
+      }
+      if (tabData.groupId && tabGroupWorkingData.get(tabData.groupId)) {
         let { groupId } = tabData;
         const tabGroup = tabGroupWorkingData.get(groupId);
         // if a tab refers to a tab group we don't know, skip any group
@@ -5020,7 +5190,10 @@ export class Tabbrowser {
               tabGroup.stateData.id,
               tabGroup.stateData.color,
               tabGroup.stateData.collapsed,
-              tabGroup.stateData.name
+              tabGroup.stateData.name,
+              tabGroup.stateData.pinned,
+              tabGroup.stateData.essential,
+              tabGroup.stateData.splitView,
             );
             tabsFragment.appendChild(tabGroup.node);
           }
@@ -5080,9 +5253,21 @@ export class Tabbrowser {
     // to remove the old selected tab.
     if (tabToSelect) {
       let leftoverTab = this.selectedTab;
+      if (this._hasAlreadyInitializedZenSessionStore || !this.documentGlobal.gZenWorkspaces.workspaceEnabled) {
       this.selectedTab = tabToSelect;
       this.removeTab(leftoverTab);
+      } else {
+        this.documentGlobal.gZenWorkspaces._tabToRemoveForEmpty = leftoverTab;
+        if (Services.prefs.getBoolPref("zen.workspaces.continue-where-left-off")) {
+          this.documentGlobal.gZenWorkspaces._tabToSelect = selectTab - 1; // -1 for the empty tab.
+        }
+        if (this.documentGlobal.gZenWorkspaces._initialTab && !this.documentGlobal.gZenVerticalTabsManager._canReplaceNewTab) {
+          this.documentGlobal.gZenWorkspaces._initialTab._shouldRemove = true;
+        }
+      }
     }
+    delete this.documentGlobal.__isNewZenWindow;
+    this._hasAlreadyInitializedZenSessionStore = true;
 
     if (tabs.length > 1 || !tabs[0].selected) {
       this.#updateTabsAfterInsert();
@@ -5313,11 +5498,17 @@ export class Tabbrowser {
     if (ownerTab) {
       tab.owner = ownerTab;
     }
+    if ((!tab.pinned && tabGroup?.isZenFolder && !Services.prefs.getBoolPref('zen.folders.owned-tabs-in-folder')) || (tabGroup && tabGroup.hasAttribute("split-view-group"))) {
+      tabGroup = null;
+    }
+    if (openerTab?.hasAttribute("zen-glance-tab")) {
+      openerTab = this.documentGlobal.gZenGlanceManager.getTabOrGlanceParent(openerTab);
+    }
 
     // Ensure we have an index if one was not provided.
     if (typeof elementIndex != "number" && typeof tabIndex != "number") {
       // Move the new tab after another tab if needed, to the end otherwise.
-      elementIndex = Infinity;
+      elementIndex = Services.prefs.getBoolPref("zen.view.show-newtab-button-top") ? this._numVisiblePinTabsWithoutCollapsed : Infinity;
       let insertRelatedAfterCurrent = Services.prefs.getBoolPref(
         "browser.tabs.insertRelatedAfterCurrent"
       );
@@ -5332,7 +5523,7 @@ export class Tabbrowser {
           (insertRelatedAfterCurrent && lastRelatedTab) ||
           openerTab ||
           this.selectedTab;
-        if (!tabGroup) {
+        if (!tabGroup && pinned === previousTab.group?.pinned) {
           tabGroup = previousTab.group;
         }
         if (
@@ -5348,7 +5539,7 @@ export class Tabbrowser {
               previousTab.splitview
             ) + 1;
         } else if (previousTab.visible) {
-          elementIndex = previousTab.elementIndex + 1;
+          elementIndex = (typeof previousTab.elementIndex === 'undefined') ? elementIndex : (previousTab.elementIndex + 1);
         } else if (previousTab == this.documentGlobal.FirefoxViewHandler.tab) {
           elementIndex = 0;
         }
@@ -5376,14 +5567,14 @@ export class Tabbrowser {
     }
     // Ensure index is within bounds.
     if (tab.pinned) {
-      index = Math.max(index, 0);
-      index = Math.min(index, this.pinnedTabCount);
+      index = Math.max(index, tab.hasAttribute("zen-essential") ? 0 : this._numZenEssentials);
+      index = Math.min(index, tab.hasAttribute("zen-essential") ? this._numZenEssentials : this._numVisiblePinTabsWithoutCollapsed);
     } else {
-      index = Math.max(index, this.pinnedTabCount);
+      index = Math.max(index, typeof elementIndex == "number" ? this._numVisiblePinTabsWithoutCollapsed : this.pinnedTabCount);
       index = Math.min(index, allItems.length);
     }
     /** @type {MozTabbrowserTab|undefined} */
-    let itemAfter = allItems.at(index);
+    let itemAfter = this.documentGlobal.gZenGlanceManager.getTabOrGlanceParent(allItems.at(index));
 
     if (pinned && !itemAfter?.pinned) {
       itemAfter = null;
@@ -5400,7 +5591,7 @@ export class Tabbrowser {
 
     this.tabContainer._invalidateCachedTabs();
 
-    if (tabGroup) {
+    if (tabGroup && !tabGroup.hasAttribute("split-view-group")) {
       if (
         (this.isTab(itemAfter) && itemAfter.group == tabGroup) ||
         this.isSplitViewWrapper(itemAfter)
@@ -5431,7 +5622,11 @@ export class Tabbrowser {
       const tabContainer = pinned
         ? this.tabContainer.pinnedTabsContainer
         : this.tabContainer;
+      if (itemAfter) {
+        itemAfter.before(tab);
+      } else {
       tabContainer.insertBefore(tab, itemAfter);
+      }
     }
 
     if (tab.group?.collapsed) {
@@ -5446,6 +5641,7 @@ export class Tabbrowser {
     if (pinned) {
       this.#updateTabBarForPinnedTabs();
     }
+    this.documentGlobal.gZenWorkspaces.fixTabInsertLocation(tab, itemAfter);
 
     this.documentGlobal.TabBarVisibility.update();
   }
@@ -6025,6 +6221,7 @@ export class Tabbrowser {
       metricsContext,
     } = {}
   ) {
+    tabs = tabs.filter(tab => !tab.hasAttribute("zen-empty-tab"));
     // When 'closeWindowWithLastTab' pref is enabled, closing all tabs
     // can be considered equivalent to closing the window.
     if (
@@ -6135,6 +6332,7 @@ export class Tabbrowser {
           closedTabCount -= 1;
         }
       }
+      this.documentGlobal.gZenUIManager.onTabClose(undefined);
 
       if (closedTabCount > 0) {
         this.recordTabMetrics(
@@ -6236,6 +6434,14 @@ export class Tabbrowser {
       return;
     }
 
+    if (this.documentGlobal.gZenWorkspaces.workspaceEnabled) {
+      let newTab = this.documentGlobal.gZenWorkspaces.handleTabBeforeClose(aTab, closeWindowWithLastTab);
+      if (newTab) {
+        this.selectedTab = newTab;
+      }
+    }
+    animate &&= !aTab.group?.hasAttribute("split-view-group");
+
     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
@@ -6244,6 +6450,9 @@ export class Tabbrowser {
     let tabWidth =
       this.documentGlobal.windowUtils.getBoundsWithoutFlushing(aTab).width;
     let isLastTab = this.#isLastTabInWindow(aTab);
+    if (this.documentGlobal.gZenGlanceManager.manageTabClose(aTab)) {
+      return;
+    }
     if (
       !this.#beginRemoveTab(aTab, {
         closeWindowFastpath: true,
@@ -6254,13 +6463,14 @@ export class Tabbrowser {
         metricsContext,
       })
     ) {
+      delete this.documentGlobal.gZenWorkspaces._isClosingWindow;
       Glean.browserTabclose.timeAnim.cancel(aTab._closeTimeAnimTimerId);
       aTab._closeTimeAnimTimerId = null;
       Glean.browserTabclose.timeNoAnim.cancel(aTab._closeTimeNoAnimTimerId);
       aTab._closeTimeNoAnimTimerId = null;
       return;
     }
-
+    this.documentGlobal.gZenWorkspaces.handleTabBeforeRemove();
     let lockTabSizing =
       !this.tabContainer.verticalMode &&
       !aTab.pinned &&
@@ -6291,7 +6501,13 @@ export class Tabbrowser {
       // We're not animating, so we can cancel the animation stopwatch.
       Glean.browserTabclose.timeAnim.cancel(aTab._closeTimeAnimTimerId);
       aTab._closeTimeAnimTimerId = null;
-      this._endRemoveTab(aTab);
+      if (animate && !this.documentGlobal.gReduceMotion && !(this.documentGlobal.gZenUIManager.testingEnabled && !this.documentGlobal.gZenUIManager.profilingEnabled)) {
+        this.documentGlobal.gZenVerticalTabsManager.animateItemClose(aTab, (animate && !this.documentGlobal.gReduceMotion)).then(() => {
+          this._endRemoveTab(aTab);
+        });
+      } else {
+        this._endRemoveTab(aTab);
+      }
       return;
     }
 
@@ -6331,7 +6547,9 @@ export class Tabbrowser {
   get #shouldCloseWindowWithLastTab() {
     return (
       !this.documentGlobal.toolbar.visible ||
-      Services.prefs.getBoolPref("browser.tabs.closeWindowWithLastTab")
+      (Services.prefs.getBoolPref("browser.tabs.closeWindowWithLastTab") &&
+        !this.documentGlobal.gZenWorkspaces._isClosingWindow &&
+        !this.documentGlobal.gZenWorkspaces._removedByStartupPage)
     );
   }
 
@@ -6347,7 +6565,7 @@ export class Tabbrowser {
    */
   #isLastTabInWindow(tab) {
     for (const otherTab of this.tabs) {
-      if (otherTab != tab && otherTab.isOpen && !otherTab.hidden) {
+      if (otherTab != tab && otherTab.isOpen && !otherTab.hidden && !otherTab.hasAttribute("zen-empty-tab")) {
         return false;
       }
     }
@@ -6488,6 +6706,7 @@ export class Tabbrowser {
 
       newTab = true;
     }
+    this.documentGlobal.gZenWorkspaces._removedByStartupPage = false;
     aTab._endRemoveArgs = [closeWindow, newTab];
 
     // swapBrowsersAndCloseOther will take care of closing the window without animation.
@@ -6542,13 +6761,7 @@ export class Tabbrowser {
     }
 
     if (newTab) {
-      this.addTrustedTab(this.documentGlobal.BROWSER_NEW_TAB_URL, {
-        skipAnimation: true,
-        // In the event that insertAfterCurrent is set and the current tab is
-        // inside a group that is being closed we want to avoid creating the
-        // new tab inside that group.
-        tabIndex: 0,
-      });
+      this.documentGlobal.gZenWorkspaces.selectEmptyTab(this.documentGlobal.BROWSER_NEW_TAB_URL);
     } else {
       this.documentGlobal.TabBarVisibility.update();
     }
@@ -6701,6 +6914,7 @@ export class Tabbrowser {
       this.tabs[i]._index = i;
     }
 
+    this.documentGlobal.gZenWorkspaces.updateTabsContainers();
     if (!this.#windowIsClosing) {
       // update tab close buttons state
       this.tabContainer._updateCloseButtons();
@@ -6891,6 +7105,7 @@ export class Tabbrowser {
       memory_after: await getTotalMemoryUsage(),
       time_to_unload_in_ms: timeElapsed,
     });
+    return true;
   }
 
   /**
@@ -6937,11 +7152,12 @@ export class Tabbrowser {
     }
 
     let excludeTabs = new Set(aExcludeTabs);
+    this.documentGlobal.gZenWorkspaces.getTabsToExclude(aTab).forEach(tab => excludeTabs.add(tab));
 
     // If this tab has a successor, it should be selectable, since
     // hiding or closing a tab removes that tab as a successor.
     if (aTab.successor && !excludeTabs.has(aTab.successor)) {
-      return aTab.successor;
+      return this.documentGlobal.gZenWorkspaces.findTabToBlur(aTab.successor);
     }
 
     if (
@@ -6949,13 +7165,13 @@ export class Tabbrowser {
       !excludeTabs.has(aTab.owner) &&
       Services.prefs.getBoolPref("browser.tabs.selectOwnerOnClose")
     ) {
-      return aTab.owner;
+      return this.documentGlobal.gZenWorkspaces.findTabToBlur(aTab.owner);
     }
 
     // Try to find a remaining tab that comes after the given tab
     let remainingTabs = Array.prototype.filter.call(
       this.visibleTabs,
-      tab => !excludeTabs.has(tab)
+      tab => !excludeTabs.has(tab) && this.documentGlobal.gZenWorkspaces._shouldChangeToTab(tab) && tab !== aTab
     );
 
     if (Services.prefs.getBoolPref("browser.tabs.selectMRUOnClose", false)) {
@@ -6970,6 +7186,13 @@ export class Tabbrowser {
       }
     }
 
+    if (remainingTabs.length > 0 && Services.prefs.getBoolPref("zen.tabs.select-recently-used-on-close")) {
+      let mostRecentTab = remainingTabs.reduce((a, b) =>
+        b.lastAccessed > a.lastAccessed ? b : a
+      );
+      return this.documentGlobal.gZenWorkspaces.findTabToBlur(mostRecentTab);
+    }
+
     let tab = this.tabContainer.findNextTab(aTab, {
       direction: 1,
       filter: _tab => remainingTabs.includes(_tab),
@@ -6983,7 +7206,7 @@ export class Tabbrowser {
     }
 
     if (tab) {
-      return tab;
+      return this.documentGlobal.gZenWorkspaces.findTabToBlur(tab);
     }
 
     // If no qualifying visible tab was found, see if there is a tab in
@@ -7004,7 +7227,7 @@ export class Tabbrowser {
       });
     }
 
-    return tab;
+    return this.documentGlobal.gZenWorkspaces.findTabToBlur(tab);
   }
 
   #blurTab(aTab) {
@@ -7021,7 +7244,7 @@ export class Tabbrowser {
    * @returns {boolean}
    *   False if swapping isn't permitted, true otherwise.
    */
-  swapBrowsersAndCloseOther(aOurTab, aOtherTab) {
+  swapBrowsersAndCloseOther(aOurTab, aOtherTab, zenCloseOther = true) {
     // Do not allow transfering a private tab to a non-private window
     // and vice versa.
     if (
@@ -7080,6 +7303,7 @@ export class Tabbrowser {
     // fire the beforeunload event in the process.  Close the other
     // window if this was its last tab.
     if (
+      zenCloseOther &&
       !remoteBrowser.#beginRemoveTab(aOtherTab, {
         adoptedByTab: aOurTab,
         closeWindowWithLastTab: true,
@@ -7091,7 +7315,7 @@ export class Tabbrowser {
     // 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.
-    let [closeWindow] = aOtherTab._endRemoveArgs;
+    let [closeWindow] = !zenCloseOther ? [false] : aOtherTab._endRemoveArgs;
     if (closeWindow) {
       let win = aOtherTab.documentGlobal;
       win.windowUtils.suppressAnimation(true);
@@ -7231,11 +7455,13 @@ export class Tabbrowser {
     }
 
     // Finish tearing down the tab that's going away.
+    if (zenCloseOther) {
     if (closeWindow) {
       aOtherTab.documentGlobal.close();
     } else {
       remoteBrowser._endRemoveTab(aOtherTab);
     }
+    }
 
     this.setTabTitle(aOurTab);
 
@@ -7484,10 +7710,10 @@ export class Tabbrowser {
     }
   }
 
-  hideTab(aTab, aSource) {
+  hideTab(aTab, aSource, forZenWorkspaces = false) {
     if (
       aTab.hidden ||
-      aTab.pinned ||
+      (aTab.pinned && !forZenWorkspaces) ||
       aTab.selected ||
       aTab.closing ||
       // Tabs that are sharing the screen, microphone or camera cannot be hidden.
@@ -7576,7 +7802,8 @@ export class Tabbrowser {
    * @param {object} [aOptions={}]
    *   Key-value pairs that will be serialized into the features string.
    */
-  replaceTabWithWindow(aTab, aOptions = {}) {
+  replaceTabWithWindow(aTab, aOptions = {}, zenForceSync = false) {
+    if (!this.isTab(aTab)) return; // TODO: Handle tab groups
     if (this.tabs.length == 1) {
       return null;
     }
@@ -7593,7 +7820,7 @@ export class Tabbrowser {
     // tell a new window to take the "dropped" tab
     let args = Cc["@mozilla.org/array;1"].createInstance(Ci.nsIMutableArray);
     args.appendElement(aTab.splitview ?? aTab);
-    return lazy.BrowserWindowTracker.openWindow({
+    let win = lazy.BrowserWindowTracker.openWindow({
       private: lazy.PrivateBrowsingUtils.isWindowPrivate(this.documentGlobal),
       features: Object.entries(aOptions)
         .map(([key, value]) => `${key}=${value}`)
@@ -7601,6 +7828,8 @@ export class Tabbrowser {
       openerWindow: this.documentGlobal,
       args,
     });
+    win._zenStartupSyncFlag = (zenForceSync || !Services.prefs.getBoolPref("zen.tabs.dnd-open-blank-window", true)) ? 'synced' : 'unsynced';
+    return win;
   }
 
   /**
@@ -7734,7 +7963,7 @@ export class Tabbrowser {
    * @returns {element is MozTabbrowserTabGroup}
    */
   isTabGroup(element) {
-    return !!(element?.tagName == "tab-group");
+    return !!(element?.tagName == "tab-group" || element?.tagName == "zen-folder");
   }
 
   /**
@@ -7807,8 +8036,8 @@ export class Tabbrowser {
     }
 
     // Don't allow mixing pinned and unpinned tabs.
-    if (this.isTab(element) && element.pinned) {
-      tabIndex = Math.min(tabIndex, this.pinnedTabCount - 1);
+    if (element.pinned) {
+      tabIndex = element.hasAttribute('zen-essential') ? Math.min(tabIndex, this._numZenEssentials - 1) : Math.min(Math.max(tabIndex, this._numZenEssentials), this.pinnedTabCount - 1);
     } else {
       tabIndex = Math.max(tabIndex, this.pinnedTabCount);
     }
@@ -7854,8 +8083,8 @@ export class Tabbrowser {
     this.#handleTabMove(
       element,
       () => {
-        let neighbor = this.tabs[tabIndex];
-        if (forceUngrouped && neighbor?.group) {
+        let neighbor = this.documentGlobal.gZenGlanceManager.getTabOrGlanceParent(this.tabs[tabIndex]);
+        if ((forceUngrouped && neighbor?.group) || neighbor?.group?.hasAttribute("split-view-group")) {
           neighbor = neighbor.group;
         }
         if (neighbor?.splitview) {
@@ -7866,6 +8095,12 @@ export class Tabbrowser {
             return;
           }
         }
+        if (element.group?.hasAttribute("split-view-group")) {
+          element = element.group;
+        }
+        if (element.group?.hasAttribute("split-view-group") && neighbor == element.group) {
+          return;
+        }
 
         if (movingForwards && neighbor) {
           neighbor.after(element);
@@ -7939,23 +8174,31 @@ export class Tabbrowser {
   ) {
     if (this.isTabGroupLabel(targetElement)) {
       targetElement = targetElement.group;
-      if (!moveBefore && !targetElement.collapsed) {
+      if (!moveBefore && !targetElement.collapsed && !targetElement.hasAttribute("split-view-group")) {
         // Right after the tab group label = before the first tab in the tab group
         targetElement = targetElement.tabs[0];
         moveBefore = true;
       }
     }
-    if (this.isTabGroupLabel(element)) {
+    if (this.isTabGroupLabel(element) || element.group?.hasAttribute("split-view-group")) {
       element = element.group;
-      if (targetElement?.group) {
-        targetElement = targetElement.group;
-      }
     }
 
     // Don't allow mixing pinned and unpinned tabs.
+    targetElement = this.documentGlobal.gZenGlanceManager.getTabOrGlanceParent(targetElement);
+    if (targetElement?.classList.contains('tab-group-label-container')) {
+      targetElement = targetElement.parentElement;
+    }
+    if (element.hasAttribute('zen-essential') && !targetElement?.hasAttribute('zen-essential')) {
+      targetElement = this.tabsWithoutGlance[this._numZenEssentials - 1];
+    } else
     if (element.pinned && !targetElement?.pinned) {
-      targetElement = this.tabs[this.pinnedTabCount - 1];
+      targetElement = this.tabsWithoutGlance[this.pinnedTabCount - 1];
       moveBefore = false;
+      if (!this.visibleTabs.includes(targetElement)) {
+        targetElement = this.documentGlobal.gZenWorkspaces.pinnedTabsContainer.querySelector('.pinned-tabs-container-separator')
+        moveBefore = true;
+      }
     } 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
@@ -7968,12 +8211,35 @@ export class Tabbrowser {
       //    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.
-      targetElement = this.tabs[this.pinnedTabCount];
+      targetElement = this.tabsWithoutGlance[this.pinnedTabCount];
       if (targetElement.group) {
         targetElement = targetElement.group;
       }
       moveBefore = true;
     }
+    if (!this.documentGlobal.gZenFolders.canDropElement(element, targetElement)) {
+      element = element.group;
+    }
+    if (!element.hasAttribute('zen-essential') && targetElement?.hasAttribute('zen-essential')) {
+      targetElement = null;
+      moveBefore = false;
+    }
+    // It is necessary to place the check below to avoid inserting an element
+    // inside when the split group is the last element.
+    if (targetElement?.group?.hasAttribute("split-view-group")) {
+      targetElement = targetElement.group;
+    }
+    if (targetElement?.hasAttribute("zen-empty-tab")) {
+      // When the folder is the last element in the pinned section,
+      // targetElement is a tab with the zen-empty-tab attribute.
+      // If the movement is from top to bottom, it must be redefined as a folder.
+      if (!moveBefore) {
+        targetElement = targetElement.group;
+      } else {
+        // Always insert an element after zen-empty-tab to avoid it moving from the first position
+        moveBefore = false;
+      }
+    }
 
     // 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.
@@ -7982,6 +8248,7 @@ export class Tabbrowser {
     }
 
     let getContainer = () =>
+      element.hasAttribute("zen-essential") ? this.documentGlobal.gZenWorkspaces.getEssentialsSection(element) :
       element.pinned
         ? this.tabContainer.pinnedTabsContainer
         : this.tabContainer;
@@ -7990,11 +8257,15 @@ export class Tabbrowser {
       element,
       () => {
         if (moveBefore) {
-          getContainer().insertBefore(element, targetElement);
+          targetElement.parentElement.insertBefore(element, targetElement);
         } else if (targetElement) {
           targetElement.after(element);
         } else {
+          if (element.pinned) {
+            getContainer().prepend(element);
+          } else {
           getContainer().appendChild(element);
+          }
         }
       },
       { metricsContext }
@@ -8070,11 +8341,15 @@ export class Tabbrowser {
    *   The context for the operation for telemetry purposes.
    */
   moveTabToExistingGroup(aTab, aGroup, { metricsContext } = {}) {
-    if (!this.isTab(aTab)) {
+    if (!this.isTab(aTab) && !aTab.hasAttribute('split-view-group')) {
       throw new Error("Can only move a tab into a tab group");
     }
-    if (aTab.pinned) {
-      return;
+    if (aTab.pinned != !!aGroup.pinned) {
+      if (aGroup.pinned) {
+        this.pinTab(aTab);
+      } else {
+        this.unpinTab(aTab);
+      }
     }
     if (aTab.group && aTab.group.id === aGroup.id) {
       return;
@@ -8153,6 +8428,7 @@ export class Tabbrowser {
 
     let state = {
       tabIndex: tab.index,
+      workspaceId: tab.getAttribute("zen-workspace-id")
     };
     if (tab.visible) {
       state.elementIndex = tab.elementIndex;
@@ -8190,7 +8466,7 @@ export class Tabbrowser {
     let changedSplitView =
       previousTabState.splitViewId != currentTabState.splitViewId;
 
-    if (changedPosition || changedTabGroup || changedSplitView) {
+    if (changedPosition || changedTabGroup || changedSplitView || (previousTabState.workspaceId != currentTabState.workspaceId)) {
       tab.dispatchEvent(
         new this.documentGlobal.CustomEvent("TabMove", {
           bubbles: true,
@@ -8248,6 +8524,10 @@ export class Tabbrowser {
 
     moveActionCallback();
 
+    this.documentGlobal.gZenWorkspaces.makeSureEmptyTabIsFirst();
+    this.documentGlobal.gZenViewSplitter._maybeRemoveFakeBrowser(false);
+    this.documentGlobal.gZenViewSplitter._canDrop = false;
+
     // Clear tabs cache after moving nodes because the order of tabs may have
     // changed.
     this.tabContainer._invalidateCachedTabs();
@@ -8307,7 +8587,22 @@ export class Tabbrowser {
    * @returns {object}
    *    The new tab in the current window, null if the tab couldn't be adopted.
    */
-  adoptTab(aTab, { elementIndex, tabIndex, selectTab = false } = {}) {
+  adoptTab(aTab, { elementIndex, tabIndex, selectTab = false, spaceId = null } = {}) {
+    if (this.documentGlobal.gZenWorkspaces.currentWindowIsSyncing && aTab.documentGlobal.gZenWorkspaces?.currentWindowIsSyncing) {
+      const tabId = aTab.id;
+      const thisTab = this.documentGlobal.gZenWindowSync.getItemFromWindow(this.documentGlobal, tabId);
+      if (thisTab) {
+        // Just move the tab to the index
+        this.moveTabTo(thisTab, { elementIndex, tabIndex });
+        if (spaceId) {
+          thisTab.setAttribute("zen-workspace-id", spaceId);
+        }
+        if (selectTab) {
+          this.selectedTab = thisTab;
+        }
+        return thisTab;
+      }
+    }
     // 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
@@ -8350,6 +8645,8 @@ export class Tabbrowser {
     }
     params.skipLoad = true;
     let newTab = this.addWebTab("about:blank", params);
+    newTab._zenContentsVisible = true;
+    newTab.zenStaticLabel = aTab.zenStaticLabel;
 
     aTab.container.tabDragAndDrop.finishAnimateTabMove();
 
@@ -9189,7 +9486,7 @@ export class Tabbrowser {
       // preventDefault(). It will still raise the window if appropriate.
       return;
     }
-    this.selectedTab = tab;
+    this.documentGlobal.gZenWorkspaces.switchTabIfNeeded(tab);
     this.documentGlobal.focus();
     aEvent.preventDefault();
   }
@@ -9206,7 +9503,6 @@ export class Tabbrowser {
 
   on_TabGroupCollapse(aEvent) {
     aEvent.target.tabs.forEach(tab => {
-      this.removeFromMultiSelectedTabs(tab);
     });
   }
 
@@ -9554,7 +9850,9 @@ export class Tabbrowser {
 
       let filter = this.#tabFilters.get(tab);
       if (filter) {
+        try {
         browser.webProgress.removeProgressListener(filter);
+        } catch {}
 
         let listener = this.#tabListeners.get(tab);
         if (listener) {
@@ -10354,6 +10652,7 @@ class TabProgressListener {
           aWebProgress.isTopLevel
         ) {
           this._tab.setAttribute("busy", "true");
+          if (!this._tab.selected) this._tab.setAttribute("unread", "true");
           this.#tabbrowser._tabAttrModified(this._tab, ["busy"]);
           this._tab._notselectedsinceload = !this._tab.selected;
         }
@@ -10434,6 +10733,7 @@ class TabProgressListener {
       // known defaults. Note we use the original URL since about:newtab
       // redirects to a prerendered page.
       const shouldRemoveFavicon =
+        !this._tab.zenStaticIcon &&
         !this._browser.mIconURL &&
         !ignoreBlank &&
         !(originalLocation.spec in FAVICON_DEFAULTS);
@@ -10610,13 +10910,6 @@ class TabProgressListener {
           this._browser.originalURI = aRequest.originalURI;
         }
 
-        if (!lazy.allowTransparentBrowser) {
-          this._browser.toggleAttribute(
-            "transparent",
-            lazy.AIWindow.isAIWindowActive(this.#documentGlobal) &&
-              lazy.AIWindow.isAIWindowContentPage(aLocation)
-          );
-        }
       }
 
       let userContextId = this._browser.getAttribute("usercontextid") || 0;