diff --git a/prefs/zen/sync.yaml b/prefs/zen/sync.yaml
deleted file mode 100644
index dff75e481..000000000
--- a/prefs/zen/sync.yaml
+++ /dev/null
@@ -1,12 +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/.
-
-- name: services.sync.engine.spaces
-  value: true
-  condition: "@IS_TWILIGHT@"
-
-- name: services.sync.engine.spaces
-  value: false
-  locked: true
-  condition: "!@IS_TWILIGHT@"
diff --git a/prefs/zen/workspaces.yaml b/prefs/zen/workspaces.yaml
index dfa8b7d6c..24aaf887c 100644
--- a/prefs/zen/workspaces.yaml
+++ b/prefs/zen/workspaces.yaml
@@ -32,6 +32,9 @@
 - name: zen.workspaces.scroll-modifier-key
   value: ctrl
 
+- name: services.sync.engine.workspaces
+  value: false
+
 - name: zen.workspaces.separate-essentials
   value: true
 
diff --git a/src/browser/components/preferences/config/account-sync-mjs.patch b/src/browser/components/preferences/config/account-sync-mjs.patch
deleted file mode 100644
index ce14b3e05..000000000
--- a/src/browser/components/preferences/config/account-sync-mjs.patch
+++ /dev/null
@@ -1,20 +0,0 @@
-diff --git a/browser/components/preferences/config/account-sync.mjs b/browser/components/preferences/config/account-sync.mjs
-index b503987a08e2ce64bfc01c4e3a21e5e19ef834f0..b1c03a0b219fd3eddd93c1deaeb18ab79c85f168 100644
---- a/browser/components/preferences/config/account-sync.mjs
-+++ b/browser/components/preferences/config/account-sync.mjs
-@@ -42,6 +42,7 @@ Preferences.addAll([
-   { id: "services.sync.engine.creditcards", type: "bool" },
-   { id: "services.sync.engine.addons", type: "bool" },
-   { id: "services.sync.engine.prefs", type: "bool" },
-+  { id: "services.sync.engine.spaces", type: "bool" },
- ]);
- 
- /**
-@@ -546,6 +547,7 @@ const SYNC_ENGINE_SETTINGS = [
-     type: "payments",
-   },
-   { id: "syncAddons", pref: "services.sync.engine.addons", type: "addons" },
-+  { id: "syncSpaces", pref: "services.sync.engine.spaces", type: "workspaces" },
-   { id: "syncSettings", pref: "services.sync.engine.prefs", type: "settings" },
- ];
- 
diff --git a/src/browser/components/preferences/dialogs/syncChooseWhatToSync-js.patch b/src/browser/components/preferences/dialogs/syncChooseWhatToSync-js.patch
index da89f90fb..e066aca21 100644
--- a/src/browser/components/preferences/dialogs/syncChooseWhatToSync-js.patch
+++ b/src/browser/components/preferences/dialogs/syncChooseWhatToSync-js.patch
@@ -6,7 +6,7 @@ index 64aa0d98a0622c01f3dcfff1a04bfcda368354d2..2013e04b0881ad2295d6897b91e1573c
    { id: "services.sync.engine.passwords", type: "bool" },
    { id: "services.sync.engine.addresses", type: "bool" },
    { id: "services.sync.engine.creditcards", type: "bool" },
-+  { id: "services.sync.engine.spaces", type: "bool" },
++  { id: "services.sync.engine.workspaces", type: "bool" },
  ]);
  
  let gSyncChooseWhatToSync = {
diff --git a/src/browser/components/preferences/dialogs/syncChooseWhatToSync-xhtml.patch b/src/browser/components/preferences/dialogs/syncChooseWhatToSync-xhtml.patch
index 0ebce7576..3b0ab370d 100644
--- a/src/browser/components/preferences/dialogs/syncChooseWhatToSync-xhtml.patch
+++ b/src/browser/components/preferences/dialogs/syncChooseWhatToSync-xhtml.patch
@@ -20,7 +20,7 @@ index a893c5ec3d007820d98f5d92dd039640faa2c181..9cbd00102e44ccf98b37845474d92d57
 +      <html:div class="sync-engine-workspaces">
 +        <checkbox
 +                data-l10n-id="sync-engine-workspaces"
-+                preference="services.sync.engine.spaces"
++                preference="services.sync.engine.workspaces"
 +        />
 +      </html:div>
      </html:div>
diff --git a/src/browser/components/preferences/sync-inc-xhtml.patch b/src/browser/components/preferences/sync-inc-xhtml.patch
index 4b6e6306d..06944335a 100644
--- a/src/browser/components/preferences/sync-inc-xhtml.patch
+++ b/src/browser/components/preferences/sync-inc-xhtml.patch
@@ -6,7 +6,7 @@ index c379e1a5f82692406a92d9fcd3bca2769dfac5b2..af037dd3d995813d966524ac44a3795d
                      <image class="sync-engine-image sync-engine-prefs" alt=""/>
                      <label data-l10n-id="sync-currently-syncing-settings"/>
                    </html:div>
-+                  <html:div engine_preference="services.sync.engine.spaces">
++                  <html:div engine_preference="services.sync.engine.workspaces">
 +                    <image class="sync-engine-image sync-engine-workspaces" alt=""/>
 +                    <label data-l10n-id="sync-currently-syncing-workspaces"/>
 +                  </html:div>
diff --git a/src/external-patches/firefox/allow_backdrop_to_work_on_transparency.patch b/src/external-patches/firefox/allow_backdrop_to_work_on_transparency.patch
deleted file mode 100644
index 20ebb535c..000000000
--- a/src/external-patches/firefox/allow_backdrop_to_work_on_transparency.patch
+++ /dev/null
@@ -1,167 +0,0 @@
-diff --git a/gfx/webrender_bindings/WebRenderAPI.cpp b/gfx/webrender_bindings/WebRenderAPI.cpp
---- a/gfx/webrender_bindings/WebRenderAPI.cpp
-+++ b/gfx/webrender_bindings/WebRenderAPI.cpp
-@@ -298,11 +298,13 @@
-                 panic_on_gl_error, picTileWidth, picTileHeight,
-                 gfx::gfxVars::WebRenderRequiresHardwareDriver(),
-                 StaticPrefs::gfx_webrender_low_quality_pinch_zoom_AtStartup(),
-                 StaticPrefs::gfx_webrender_max_shared_surface_size_AtStartup(),
-                 StaticPrefs::gfx_webrender_enable_subpixel_aa_AtStartup(),
--                compositor->ShouldUseLayerCompositor())) {
-+                compositor->ShouldUseLayerCompositor(),
-+                StaticPrefs::
-+                    gfx_webrender_opaque_backdrop_fallback_AtStartup())) {
-           // wr_window_new puts a message into gfxCriticalNote if it returns
-           // false
-           MOZ_ASSERT(errorMessage);
-           error.AssignASCII(errorMessage);
-           wr_api_free_error_msg(errorMessage);
-diff --git a/gfx/webrender_bindings/src/bindings.rs b/gfx/webrender_bindings/src/bindings.rs
---- a/gfx/webrender_bindings/src/bindings.rs
-+++ b/gfx/webrender_bindings/src/bindings.rs
-@@ -1998,10 +1998,11 @@
-     reject_software_rasterizer: bool,
-     low_quality_pinch_zoom: bool,
-     max_shared_surface_size: i32,
-     enable_subpixel_aa: bool,
-     use_layer_compositor: bool,
-+    opaque_backdrop_fallback: bool,
- ) -> bool {
-     assert!(unsafe { is_in_render_thread() });
- 
-     // Ensure the WR profiler callbacks are hooked up to the Gecko profiler.
-     set_profiler_hooks(Some(&PROFILER_HOOKS));
-@@ -2164,10 +2165,11 @@
-         texture_cache_config,
-         reject_software_rasterizer,
-         low_quality_pinch_zoom,
-         max_shared_surface_size,
-         enable_dithering,
-+        opaque_backdrop_fallback,
-         ..Default::default()
-     };
- 
-     let window_size = DeviceIntSize::new(window_width, window_height);
-     let notifier = Box::new(CppNotifier { window_id });
-diff --git a/gfx/wr/webrender/src/device/gl.rs b/gfx/wr/webrender/src/device/gl.rs
---- a/gfx/wr/webrender/src/device/gl.rs
-+++ b/gfx/wr/webrender/src/device/gl.rs
-@@ -3982,10 +3982,14 @@
- 
-     pub fn disable_color_write(&self) {
-         self.gl.color_mask(false, false, false, false);
-     }
- 
-+    pub fn set_color_mask(&self, r: bool, g: bool, b: bool, a: bool) {
-+        self.gl.color_mask(r, g, b, a);
-+    }
-+
-     pub fn set_blend(&mut self, enable: bool) {
-         if enable {
-             self.gl.enable(gl::BLEND);
-         } else {
-             self.gl.disable(gl::BLEND);
-diff --git a/gfx/wr/webrender/src/renderer/init.rs b/gfx/wr/webrender/src/renderer/init.rs
---- a/gfx/wr/webrender/src/renderer/init.rs
-+++ b/gfx/wr/webrender/src/renderer/init.rs
-@@ -204,6 +204,8 @@
-     pub low_quality_pinch_zoom: bool,
-     pub max_shared_surface_size: i32,
-     /// If true, open a debug socket to listen for remote debugger.
-     /// Relies on `debugger` cargo feature being enabled.
-     pub enable_debugger: bool,
-+    /// See explanation of `gfx.webrender.opaque-backdrop-fallback`.
-+    pub opaque_backdrop_fallback: bool,
- }
-@@ -277,9 +279,10 @@
-             enable_instancing: true,
-             reject_software_rasterizer: false,
-             low_quality_pinch_zoom: false,
-             max_shared_surface_size: 2048,
-             enable_debugger: true,
-+            opaque_backdrop_fallback: false,
-         }
-     }
- }
- 
-@@ -802,10 +805,11 @@
-         allocated_native_surfaces: FastHashSet::default(),
-         debug_overlay_state: DebugOverlayState::new(),
-         buffer_damage_tracker: BufferDamageTracker::default(),
-         max_primitive_instance_count,
-         enable_instancing: options.enable_instancing,
-+        opaque_backdrop_fallback: options.opaque_backdrop_fallback,
-         consecutive_oom_frames: 0,
-         target_frame_publish_id: None,
-         pending_result_msg: None,
-         layer_compositor_frame_state_in_prev_frame: None,
-         external_composite_debug_items: Vec::new(),
-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 @@
-     buffer_damage_tracker: BufferDamageTracker,
- 
-     max_primitive_instance_count: usize,
-     enable_instancing: bool,
- 
-+    opaque_backdrop_fallback: bool,
-+
-     /// Count consecutive oom frames to detectif we are stuck unable to render
-     /// in a loop.
-     consecutive_oom_frames: u32,
- 
-     /// update() defers processing of ResultMsg, if frame_publish_id of
-@@ -2787,18 +2789,29 @@
-                 let read_target = ReadTarget::from_texture(cache_texture);
- 
-                 // Should always be drawing to picture cache tiles or off-screen surface!
-                 debug_assert!(!draw_target.is_default());
-                 let device_to_framebuffer = Scale::new(1i32);
-+                let dest_fb_rect = dest * device_to_framebuffer;
- 
-                 self.device.blit_render_target(
-                     read_target,
-                     src * device_to_framebuffer,
-                     draw_target,
--                    dest * device_to_framebuffer,
-+                    dest_fb_rect,
-                     TextureFilter::Linear,
-                 );
-+
-+                if self.opaque_backdrop_fallback {
-+                    self.device.set_color_mask(false, false, false, true);
-+                    self.device.clear_target(
-+                        Some([0.0, 0.0, 0.0, 1.0]),
-+                        None,
-+                        Some(dest_fb_rect),
-+                    );
-+                    self.device.set_color_mask(true, true, true, true);
-+                }
-             }
-         }
-     }
- 
-     fn draw_picture_cache_target(
-diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
---- a/modules/libpref/init/StaticPrefList.yaml
-+++ b/modules/libpref/init/StaticPrefList.yaml
-@@ -8439,10 +8439,17 @@
- #else
-   value: false
- #endif
-   mirror: once
- 
-+# Make backdrop-filter treat its captured backdrop as if it had been
-+# composited over an opaque-black background. (See bug 2036640)
-+- name: gfx.webrender.opaque-backdrop-fallback
-+  type: bool
-+  value: true
-+  mirror: once
-+
- # Disable wait of GPU execution completion
- - name: gfx.webrender.wait-gpu-finished.disabled
-   type: bool
-   value: false
-   mirror: once
-
diff --git a/src/services/sync/modules/service-sys-mjs.patch b/src/services/sync/modules/service-sys-mjs.patch
deleted file mode 100644
index daf57720d..000000000
--- a/src/services/sync/modules/service-sys-mjs.patch
+++ /dev/null
@@ -1,15 +0,0 @@
-diff --git a/services/sync/modules/service.sys.mjs b/services/sync/modules/service.sys.mjs
-index 4f4efe572909441abdd81909282936702c225621..81ab06a9414ed656b644a21b40b683f06a4f8dbf 100644
---- a/services/sync/modules/service.sys.mjs
-+++ b/services/sync/modules/service.sys.mjs
-@@ -99,6 +99,10 @@ function getEngineModules() {
-     whenTrue: "ExtensionStorageEngineKinto",
-     whenFalse: "ExtensionStorageEngineBridge",
-   };
-+  result.Spaces = {
-+    module: "resource:///modules/zen/ZenWorkspacesSync.sys.mjs",
-+    symbol: "ZenWorkspacesEngine",
-+  };
-   return result;
- }
- 
diff --git a/src/toolkit/components/contextualidentity/ContextualIdentityService-sys-mjs.patch b/src/toolkit/components/contextualidentity/ContextualIdentityService-sys-mjs.patch
deleted file mode 100644
index 1b108254d..000000000
--- a/src/toolkit/components/contextualidentity/ContextualIdentityService-sys-mjs.patch
+++ /dev/null
@@ -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
diff --git a/src/zen/moz.build b/src/zen/moz.build
index 4e3e80ecb..8b1426065 100644
--- a/src/zen/moz.build
+++ b/src/zen/moz.build
@@ -20,5 +20,4 @@ DIRS += [
     "share",
     "spaces",
     "space-routing",
-    "sync",
 ]
diff --git a/src/zen/sessionstore/ZenSessionManager.sys.mjs b/src/zen/sessionstore/ZenSessionManager.sys.mjs
index bccec81c6..39f2d0eb2 100644
--- 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",
@@ -610,7 +609,6 @@ export class nsZenSessionManager {
       }
     );
     this.#collectWindowData(windows);
-    lazy.ZenSyncStore.notifyAboutChanges();
     // This would save the data to disk asynchronously or when quitting the app.
     let sidebar = this.#sidebarWithoutCloning;
     this.#file.data = sidebar;
@@ -624,15 +622,6 @@ export class nsZenSessionManager {
     this.log(`Saving Zen session data with ${sidebar.tabs?.length || 0} tabs`);
   }
 
-  /**
-   * Returns the sidebar data object.
-   *
-   * @returns {object}
-   */
-  getSidebarData() {
-    return this.#sidebarWithoutCloning;
-  }
-
   /**
    * Called when the last known backup should be deleted and a new one
    * created. This uses the #deferredBackupTask to debounce clusters of
diff --git a/src/zen/spaces/ZenSpaceManager.mjs b/src/zen/spaces/ZenSpaceManager.mjs
index 78d990899..beae4b055 100644
--- 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", () => {
@@ -149,7 +148,7 @@ class nsZenWorkspaces {
     if (!this.privateWindowOrDisabled) {
       const observerFunction = async () => {
         delete this._workspaceBookmarksCache;
-        await this.#initializeWorkspaceBookmarks();
+        await this.workspaceBookmarks();
         this._invalidateBookmarkContainers();
       };
       Services.obs.addObserver(observerFunction, "workspace-bookmarks-updated");
@@ -169,63 +168,6 @@ 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(() => {
@@ -752,17 +694,17 @@ class nsZenWorkspaces {
     return spacesForSS;
   }
 
-  async #initializeWorkspaceBookmarks() {
+  async workspaceBookmarks() {
     if (this.privateWindowOrDisabled) {
       this._workspaceBookmarksCache = {
         bookmarks: [],
         lastChangeTimestamp: 0,
       };
-      return;
+      return this._workspaceBookmarksCache;
     }
 
     if (this._workspaceBookmarksCache) {
-      return;
+      return this._workspaceBookmarksCache;
     }
 
     const [bookmarks, lastChangeTimestamp] = await Promise.all([
@@ -771,6 +713,8 @@ class nsZenWorkspaces {
     ]);
 
     this._workspaceBookmarksCache = { bookmarks, lastChangeTimestamp };
+
+    return this._workspaceCache;
   }
 
   restoreWorkspacesFromSessionStore(aWinData = {}) {
@@ -830,7 +774,7 @@ class nsZenWorkspaces {
     return (async () => {
       await this.#waitForPromises();
       this.#afterLoadInit();
-      await this.#initializeWorkspaceBookmarks();
+      await this.workspaceBookmarks();
       await this.changeWorkspace(activeWorkspace, { onInit: true });
       this.#fixTabPositions();
       this.onWindowResize();
@@ -856,13 +800,6 @@ class nsZenWorkspaces {
     })();
   }
 
-  #markWorkspaceChanged(workspaceId) {
-    lazy.ZenSyncStore.markItemChanged({
-      type: "space",
-      id: workspaceId,
-    });
-  }
-
   async selectStartPage() {
     if (!this.workspaceEnabled || gZenUIManager.testingEnabled) {
       return;
@@ -1283,19 +1220,12 @@ class nsZenWorkspaces {
     } else {
       workspacesData.push(workspaceData);
     }
-    // mark item as changed for sync
-    this.#markWorkspaceChanged(workspaceData.uuid);
-
     this.#propagateWorkspaceData();
   }
 
   removeWorkspace(windowID) {
     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(
@@ -1427,50 +1357,30 @@ class nsZenWorkspaces {
     if (this.privateWindowOrDisabled) {
       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 workspaces = this._workspaceCache;
     const workspace = workspaces.find(w => w.uuid === id);
     if (!workspace) {
       console.warn(`Workspace with ID ${id} not found for reordering.`);
       return;
     }
-
     // Remove the workspace from its current position
     const currentIndex = workspaces.indexOf(workspace);
     if (currentIndex === -1) {
       console.warn(`Workspace with ID ${id} not found in the list.`);
       return;
     }
-
+    workspaces.splice(currentIndex, 1);
     // Insert the workspace at the new position
-    if (newPosition < 0 || newPosition >= workspaces.length) {
+    if (newPosition < 0 || newPosition > workspaces.length) {
       console.warn(
         `Invalid position ${newPosition} for reordering workspace with ID ${id}.`
       );
       return;
     }
-
-    workspaces.splice(currentIndex, 1);
     workspaces.splice(newPosition, 0, workspace);
-
     // 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);
+      this.#propagateWorkspaceData();
     }
   }
 
@@ -2443,7 +2353,7 @@ class nsZenWorkspaces {
       for (const tab of gBrowser.tabs) {
         if (
           !tab.hasAttribute("zen-workspace-id") &&
-          !tab.hasAttribute("zen-essential")
+          !tab.hasAttribute("zen-workspace-id")
         ) {
           tab.setAttribute("zen-workspace-id", workspace.uuid);
         }
diff --git a/src/zen/sync/ZenSyncManager.sys.mjs b/src/zen/sync/ZenSyncManager.sys.mjs
deleted file mode 100644
index 1b454da81..000000000
--- a/src/zen/sync/ZenSyncManager.sys.mjs
+++ /dev/null
@@ -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();
diff --git a/src/zen/sync/ZenWorkspacesSync.sys.mjs b/src/zen/sync/ZenWorkspacesSync.sys.mjs
deleted file mode 100644
index 0b0946ed4..000000000
--- a/src/zen/sync/ZenWorkspacesSync.sys.mjs
+++ /dev/null
@@ -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;
-  }
-}
diff --git a/src/zen/sync/moz.build b/src/zen/sync/moz.build
deleted file mode 100644
index d10ad7a19..000000000
--- a/src/zen/sync/moz.build
+++ /dev/null
@@ -1,8 +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/.
-
-EXTRA_JS_MODULES.zen += [
-  "ZenSyncManager.sys.mjs",
-  "ZenWorkspacesSync.sys.mjs",
-]
diff --git a/tools/ffprefs/src/main.rs b/tools/ffprefs/src/main.rs
index 20724730d..ac11c8e5b 100644
--- a/tools/ffprefs/src/main.rs
+++ b/tools/ffprefs/src/main.rs
@@ -346,17 +346,6 @@ fn expand_pref_values(prefs: &mut [Preference]) {
             }
             pref.value = new_value.clone();
         }
-        // Also change the condition if it contains placeholders
-        if let Some(condition) = &pref.condition {
-            let mut new_condition = condition.clone();
-            for (key, value) in &env_values {
-                let placeholder = format!("@{}@", key);
-                if new_condition.contains(&placeholder) {
-                    new_condition = new_condition.replace(&placeholder, if *value { "1" } else { "0" });
-                }
-                pref.condition = Some(new_condition.clone());
-            }
-        }
     }
 }