diff --git a/browser/components/tabbrowser/content/tabbrowser.js b/browser/components/tabbrowser/content/tabbrowser.js
index 628aa6596627c85efe361fc1ece8fd58f7ee653e..091194c85e35743c648f043a5fb7c8f7472158f2 100644
--- a/browser/components/tabbrowser/content/tabbrowser.js
+++ b/browser/components/tabbrowser/content/tabbrowser.js
@@ -412,11 +412,50 @@
       return this.tabContainer.visibleTabs;
     }
 
+    get _numVisiblePinTabs() {
+      let i = 0;
+      for (let tab of this.tabs) {
+        if (!tab.pinned && !tab.hasAttribute("zen-glance-tab")) {
+          break;
+        }
+        if (!tab.hidden) {
+          i += !tab.hasAttribute("zen-glance-tab");
+        }
+      }
+      return i;
+    }
+
+    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 _numZenVisibleEssentials() {
+      let i = 0;
+      for (let tab of this.tabs) {
+        if (!tab.hasAttribute("zen-essential") && !tab.hasAttribute("zen-glance-tab")) {
+          break;
+        }
+        if (!tab.hidden) {
+          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;
     }
@@ -814,7 +853,7 @@
       this.ungroupTab(aTab);
       if (this.tabContainer.verticalMode) {
         this._handleTabMove(aTab, () =>
-          this.verticalPinnedTabsContainer.appendChild(aTab)
+          aTab.hasAttribute("zen-essential") ? document.getElementById("zen-essentials-container").appendChild(aTab) : this.verticalPinnedTabsContainer.insertBefore(aTab, this.verticalPinnedTabsContainer.lastChild)
         );
       } else {
         this.moveTabTo(aTab, this.pinnedTabCount, { forceStandaloneTab: true });
@@ -835,7 +874,7 @@
           // the moving of a tab from the vertical pinned tabs container
           // and back into arrowscrollbox.
           aTab.removeAttribute("pinned");
-          this.tabContainer.arrowScrollbox.prepend(aTab);
+          ZenWorkspaces.activeWorkspaceStrip.prepend(aTab);
         });
       } else {
         this.moveTabTo(aTab, this.pinnedTabCount - 1, {
@@ -1018,6 +1057,8 @@
 
       let LOCAL_PROTOCOLS = ["chrome:", "about:", "resource:", "data:"];
 
+      try {
+      gZenPinnedTabManager.onTabIconChanged(aTab, aIconURL);
       if (
         aIconURL &&
         !aLoadingPrincipal &&
@@ -1028,6 +1069,9 @@
         );
         return;
       }
+      } catch (e) {
+        console.warn(e);
+      }
 
       let browser = this.getBrowserForTab(aTab);
       browser.mIconURL = aIconURL;
@@ -1273,6 +1317,7 @@
       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.ownerGlobal == BrowserWindowTracker.getTopWindow()) {
@@ -1425,6 +1470,9 @@
       }
 
       let activeEl = document.activeElement;
+      if (gURLBar._zenHandleUrlbarClose) {
+        gURLBar._zenHandleUrlbarClose(true);
+      }
       // If focus is on the old tab, move it to the new tab.
       if (activeEl == oldTab) {
         newTab.focus();
@@ -1748,7 +1796,7 @@
     }
 
     _setTabLabel(aTab, aLabel, { beforeTabOpen, isContentTitle, isURL } = {}) {
-      if (!aLabel || aLabel.includes("about:reader?")) {
+      if (!aLabel || aLabel.includes("about:reader?") || aTab.hasAttribute("zen-has-static-label")) {
         return false;
       }
 
@@ -1851,7 +1899,7 @@
         newIndex = this.selectedTab._tPos + 1;
       }
 
-      if (replace) {
+      if (replace && !(!targetTab && this.selectedTab?.hasAttribute('zen-empty-tab'))) {
         let browser;
         if (targetTab) {
           browser = this.getBrowserForTab(targetTab);
@@ -2108,6 +2156,7 @@
       uriIsAboutBlank,
       userContextId,
       skipLoad,
+      _forZenEmptyTab,
     } = {}) {
       let b = document.createXULElement("browser");
       // Use the JSM global to create the permanentKey, so that if the
@@ -2181,8 +2230,7 @@
         // we use a different attribute name for this?
         b.setAttribute("name", name);
       }
-
-      if (this._allowTransparentBrowser) {
+      if (this._allowTransparentBrowser || _forZenEmptyTab) {
         b.setAttribute("transparent", "true");
       }
 
@@ -2347,7 +2395,7 @@
 
       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.
@@ -2406,8 +2454,8 @@
       // 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) {
-        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;
       }
@@ -2629,6 +2677,7 @@
         schemelessInput,
         hasValidUserGestureActivation = false,
         textDirectiveUserActivation = false,
+        _forZenEmptyTab,
       } = {}
     ) {
       // all callers of addTab that pass a params object need to pass
@@ -2639,6 +2688,12 @@
         );
       }
 
+      let hasZenDefaultUserContextId = false;
+      let zenForcedWorkspaceId = undefined;
+      if (typeof ZenWorkspaces !== "undefined") {
+        [userContextId, hasZenDefaultUserContextId, zenForcedWorkspaceId] = ZenWorkspaces.getContextIdIfNeeded(userContextId, fromExternal, allowInheritPrincipal);
+      }
+
       if (!UserInteraction.running("browser.tabs.opening", window)) {
         UserInteraction.start("browser.tabs.opening", "initting", window);
       }
@@ -2702,6 +2757,15 @@
           noInitialLabel,
           skipBackgroundNotify,
         });
+        if (hasZenDefaultUserContextId) {
+          t.setAttribute("zenDefaultUserContextId", "true");
+        }
+        if (zenForcedWorkspaceId !== undefined) {
+          t.setAttribute("zen-workspace-id", zenForcedWorkspaceId);
+        }
+        if (_forZenEmptyTab) {
+          t.setAttribute("zen-empty-tab", "true");
+        }
         if (insertTab) {
           // insert the tab into the tab container in the correct position
           this._insertTabAtIndex(t, {
@@ -2726,6 +2790,7 @@
           initialBrowsingContextGroupId,
           openWindowInfo,
           skipLoad,
+          _forZenEmptyTab,
         }));
 
         if (focusUrlBar) {
@@ -2845,6 +2910,9 @@
         }
       }
 
+      if (typeof window.gZenVerticalTabsManager !== "undefined") {
+        gZenVerticalTabsManager.animateTab(t);
+      }
       // Additionally send pinned tab events
       if (pinned) {
         this._notifyPinnedStatus(t);
@@ -2918,7 +2986,8 @@
         id = `${Date.now()}-${Math.round(Math.random() * 100)}`;
       }
       let group = this._createTabGroup(id, color, false, label);
-      this.tabContainer.insertBefore(
+      group.pinned = tabs.some(tab => tab.pinned);
+      (group.pinned ? this.verticalPinnedTabsContainer : this.tabContainer).insertBefore(
         group,
         insertBefore?.group ?? insertBefore
       );
@@ -3126,6 +3195,7 @@
         initialBrowsingContextGroupId,
         openWindowInfo,
         skipLoad,
+        _forZenEmptyTab
       }
     ) {
       // If we don't have a preferred remote type, and we have a remote
@@ -3189,6 +3259,7 @@
           openWindowInfo,
           name,
           skipLoad,
+          _forZenEmptyTab
         });
       }
 
@@ -3367,6 +3438,24 @@
         ) {
           tabWasReused = true;
           tab = this.selectedTab;
+          if (tabData.zenWorkspace) {
+            tab.setAttribute("zen-workspace-id", tabData.zenWorkspace);
+          }
+          if (tabData.zenIsEmpty) {
+            tab.setAttribute("zen-empty-tab", "true");
+          }
+          if (tabData.zenPinnedId) {
+            tab.setAttribute("zen-pin-id", tabData.zenPinnedId);
+          }
+          if (tabData.zenEssential) {
+            tab.setAttribute("zen-essential", "true");
+          }
+          if (tabData.zenDefaultUserContextId) {
+            tab.setAttribute("zenDefaultUserContextId", "true");
+          }
+          if (tabData.zenPinnedEntry) {
+            tab.setAttribute("zen-pinned-entry", tabData.zenPinnedEntry);
+          }
           if (!tabData.pinned) {
             this.unpinTab(tab);
           } else {
@@ -3380,6 +3469,7 @@
             restoreTabsLazily && !select && !tabData.pinned;
 
           let url = "about:blank";
+          gZenPinnedTabManager.resetPinnedTabData(tabData);
           if (tabData.entries?.length) {
             let activeIndex = (tabData.index || tabData.entries.length) - 1;
             // Ensure the index is in bounds.
@@ -3415,7 +3505,24 @@
             skipLoad: true,
             preferredRemoteType,
           });
-
+          if (tabData.zenWorkspace) {
+            tab.setAttribute("zen-workspace-id", tabData.zenWorkspace);
+          }
+          if (tabData.zenPinnedId) {
+            tab.setAttribute("zen-pin-id", tabData.zenPinnedId);
+          }
+          if (tabData.zenIsEmpty) {
+            tab.setAttribute("zen-empty-tab", "true");
+          }
+          if (tabData.zenEssential) {
+            tab.setAttribute("zen-essential", "true");
+          }
+          if (tabData.zenDefaultUserContextId) {
+            tab.setAttribute("zenDefaultUserContextId", "true");
+          }
+          if (tabData.zenPinnedEntry) {
+            tab.setAttribute("zen-pinned-entry", tabData.zenPinnedEntry);
+          }
           if (select) {
             tabToSelect = tab;
           }
@@ -3428,8 +3535,8 @@
           // inserted in the DOM. If the tab is not yet in the DOM,
           // just insert it in the right place from the start.
           if (!tab.parentNode) {
-            tab._tPos = this.pinnedTabCount;
-            this.tabContainer.insertBefore(tab, this.tabs[this.pinnedTabCount]);
+            tab._tPos = this._numVisiblePinTabs;
+            this.tabContainer.insertBefore(tab, this.tabs[this._numVisiblePinTabs]);
             tab.toggleAttribute("pinned", true);
             this.tabContainer._invalidateCachedTabs();
             // Then ensure all the tab open/pinning information is sent.
@@ -3693,7 +3800,7 @@
       // Ensure we have an index if one was not provided.
       if (typeof index != "number") {
         // Move the new tab after another tab if needed, to the end otherwise.
-        index = Infinity;
+        index = Services.prefs.getBoolPref("zen.view.show-newtab-button-top") ? this.pinnedTabCount : Infinity;
         if (
           !bulkOrderedOpen &&
           ((openerTab &&
@@ -3736,18 +3843,18 @@
 
       // 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.pinnedTabCount);
       } else {
         index = Math.max(index, this.pinnedTabCount);
         index = Math.min(index, this.tabs.length);
       }
 
       /** @type {MozTabbrowserTab|undefined} */
-      let tabAfter = this.tabs.at(index);
+      let tabAfter = this.tabs.filter(tab => !tab.hasAttribute("zen-glance-tab")).at(index);
       this.tabContainer._invalidateCachedTabs();
 
-      if (tabGroup) {
+      if (tabGroup && !tabGroup.hasAttribute("split-view-group")) {
         if (tabAfter && tabAfter.group == tabGroup) {
           // Place at the front of, or between tabs in, the same tab group
           this.tabContainer.insertBefore(tab, tabAfter);
@@ -4059,6 +4166,9 @@
         return;
       }
 
+      for (let tab of selectedTabs) {
+        gZenPinnedTabManager._removePinnedAttributes(tab, true);
+      }
       this.removeTabs(selectedTabs);
     }
 
@@ -4391,6 +4501,7 @@
         skipSessionStore,
       } = {}
     ) {
+      gZenUIManager.saveScrollbarState();
       if (UserInteraction.running("browser.tabs.opening", window)) {
         UserInteraction.finish("browser.tabs.opening", window);
       }
@@ -4407,6 +4518,12 @@
         TelemetryStopwatch.start("FX_TAB_CLOSE_TIME_NO_ANIM_MS", aTab);
       }
 
+      if (ZenWorkspaces.workspaceEnabled) {
+        let newTab = ZenWorkspaces.handleTabBeforeClose(aTab);
+        if (newTab) {
+          this.selectedTab = newTab;
+        }
+      }
       // Handle requests for synchronously removing an already
       // asynchronously closing tab.
       if (!animate && aTab.closing) {
@@ -4421,7 +4538,9 @@
       // frame created for it (for example, by updating the visually selected
       // state).
       let tabWidth = window.windowUtils.getBoundsWithoutFlushing(aTab).width;
-
+      if (gZenGlanceManager.manageTabClose(aTab)) {
+        return;
+      }
       if (
         !this._beginRemoveTab(aTab, {
           closeWindowFastpath: true,
@@ -4435,7 +4554,6 @@
         TelemetryStopwatch.cancel("FX_TAB_CLOSE_TIME_NO_ANIM_MS", aTab);
         return;
       }
-
       let lockTabSizing =
         !this.tabContainer.verticalMode &&
         !aTab.pinned &&
@@ -4574,14 +4692,14 @@
         !!this.tabsInCollapsedTabGroups.length;
       if (
         aTab.visible &&
-        this.visibleTabs.length == 1 &&
+        this.visibleTabs.length == 1 && !aTab._closingGlance &&
         !anyRemainingTabsInCollapsedTabGroups
       ) {
         closeWindow =
           closeWindowWithLastTab != null
             ? closeWindowWithLastTab
             : !window.toolbar.visible ||
-              Services.prefs.getBoolPref("browser.tabs.closeWindowWithLastTab");
+              Services.prefs.getBoolPref("browser.tabs.closeWindowWithLastTab") && !ZenWorkspaces._isClosingWindow && !ZenWorkspaces._removedByStartupPage;
 
         if (closeWindow) {
           // We've already called beforeunload on all the relevant tabs if we get here,
@@ -4605,6 +4723,7 @@
 
         newTab = true;
       }
+      ZenWorkspaces._removedByStartupPage = false;
       aTab._endRemoveArgs = [closeWindow, newTab];
 
       // swapBrowsersAndCloseOther will take care of closing the window without animation.
@@ -4645,9 +4764,7 @@
       aTab._mouseleave();
 
       if (newTab) {
-        this.addTrustedTab(BROWSER_NEW_TAB_URL, {
-          skipAnimation: true,
-        });
+        ZenWorkspaces.selectEmptyTab();
       } else {
         TabBarVisibility.update();
       }
@@ -4776,6 +4893,8 @@
         this.tabs[i]._tPos = i;
       }
 
+      ZenWorkspaces.updateTabsContainers();
+
       if (!this._windowIsClosing) {
         if (wasPinned) {
           this.tabContainer._positionPinnedTabs();
@@ -4994,7 +5113,7 @@
         !excludeTabs.has(aTab.owner) &&
         Services.prefs.getBoolPref("browser.tabs.selectOwnerOnClose")
       ) {
-        return aTab.owner;
+        return ZenWorkspaces.findTabToBlur(aTab.owner);
       }
 
       // Try to find a remaining tab that comes after the given tab
@@ -5016,7 +5135,7 @@
       }
 
       if (tab) {
-        return tab;
+        return ZenWorkspaces.findTabToBlur(tab);
       }
 
       // If no qualifying visible tab was found, see if there is a tab in
@@ -5434,10 +5553,10 @@
       SessionStore.deleteCustomTabValue(aTab, "hiddenBy");
     }
 
-    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.
@@ -5675,7 +5794,7 @@
 
       // Don't allow mixing pinned and unpinned tabs.
       if (aTab.pinned) {
-        aIndex = Math.min(aIndex, this.pinnedTabCount - 1);
+        aIndex = aTab.hasAttribute('zen-essential') ? Math.min(aIndex, this._numZenEssentials - 1) : Math.min(aIndex, this.pinnedTabCount - 1);
       } else {
         aIndex = Math.max(aIndex, this.pinnedTabCount);
       }
@@ -5684,11 +5803,17 @@
       }
 
       this._handleTabMove(aTab, () => {
-        let neighbor = this.tabs[aIndex];
-        if (forceStandaloneTab && neighbor.group) {
+        let neighbor = this.tabs.filter(tab => !tab.hasAttribute("zen-glance-tab"))[aIndex];
+        const _tPos = aTab._tPos;
+        if ((forceStandaloneTab && neighbor.group) || neighbor.group?.hasAttribute("split-view-group")) {
           neighbor = neighbor.group;
+        } else if (aTab.group && aTab.group.hasAttribute("split-view-group")) {
+          aTab = aTab.group;
+        }
+        if (aTab.group?.hasAttribute("split-view-group") && neighbor == aTab.group) {
+          return;
         }
-        if (neighbor && aIndex >= aTab._tPos) {
+        if (neighbor && aIndex >= _tPos) {
           neighbor.after(aTab);
         } else {
           this.tabContainer.insertBefore(aTab, neighbor);
@@ -5697,7 +5822,7 @@
     }
 
     moveTabToGroup(aTab, aGroup) {
-      if (aTab.pinned) {
+      if (aTab.pinned != !!aGroup.pinned && !aTab.hasAttribute("zen-essential")) {
         return;
       }
       if (aTab.group && aTab.group.id === aGroup.id) {
@@ -5721,6 +5846,8 @@
 
       moveActionCallback();
 
+      ZenWorkspaces._makeSureEmptyTabIsLast();
+
       // Clear tabs cache after moving nodes because the order of tabs may have
       // changed.
       this.tabContainer._invalidateCachedTabs();
@@ -5771,7 +5898,7 @@
         createLazyBrowser,
       };
 
-      let numPinned = this.pinnedTabCount;
+      let numPinned = this._numVisiblePinTabs;
       if (aIndex < numPinned || (aTab.pinned && aIndex == numPinned)) {
         params.pinned = true;
       }
@@ -7415,6 +7542,7 @@
             aWebProgress.isTopLevel
           ) {
             this.mTab.setAttribute("busy", "true");
+            if (!this.mTab.selected) this.mTab.setAttribute("unread", "true");
             gBrowser._tabAttrModified(this.mTab, ["busy"]);
             this.mTab._notselectedsinceload = !this.mTab.selected;
           }
@@ -8381,7 +8509,7 @@ var TabContextMenu = {
     );
     contextUnpinSelectedTabs.hidden =
       !this.contextTab.pinned || !multiselectionContext;
-
+    gZenPinnedTabManager.updatePinnedTabContextMenu(this.contextTab);
     // Move Tab items
     let contextMoveTabOptions = document.getElementById(
       "context_moveTabOptions"
@@ -8414,7 +8542,7 @@ var TabContextMenu = {
     let contextMoveTabToStart = document.getElementById("context_moveToStart");
     let isFirstTab =
       tabsToMove[0] == visibleTabs[0] ||
-      tabsToMove[0] == visibleTabs[gBrowser.pinnedTabCount];
+      tabsToMove[0] == visibleTabs[gBrowser._numVisiblePinTabs];
     contextMoveTabToStart.disabled = isFirstTab && allSelectedTabsAdjacent;
 
     document.getElementById("context_openTabInWindow").disabled =
@@ -8647,6 +8775,7 @@ var TabContextMenu = {
     if (this.contextTab.multiselected) {
       gBrowser.removeMultiSelectedTabs();
     } else {
+      gZenPinnedTabManager._removePinnedAttributes(this.contextTab, true);
       gBrowser.removeTab(this.contextTab, { animate: true });
     }
   },