diff --git a/browser/components/tabbrowser/content/tabbrowser.js b/browser/components/tabbrowser/content/tabbrowser.js
index ce68c339f35416574b7bc7ebf8c93378f653242b..394f76f94cc70314da37941062f8cf011a858e03 100644
--- a/browser/components/tabbrowser/content/tabbrowser.js
+++ b/browser/components/tabbrowser/content/tabbrowser.js
@@ -409,11 +409,39 @@
       return count;
     }
 
+    get _numVisiblePinTabs() {
+      let i = 0;
+      for (let tab of this.tabs) {
+        if (!tab.pinned) {
+          break;
+        }
+        if (!tab.hidden) {
+          i++;
+        }
+      }
+      return i;
+    }
+
+    get _numZenEssentials() {
+      let i = 0;
+      for (let tab of this.tabs) {
+        if (!tab.hasAttribute("zen-essential")) {
+          break;
+        }
+        if (!tab.hidden) {
+          i++;
+        }
+      }
+      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) {
           break;
         }
+        i++;
       }
       return i;
     }
@@ -806,7 +834,7 @@
       this.showTab(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.appendChild(aTab)
         );
       } else {
         this.moveTabTo(aTab, this.pinnedTabCount);
@@ -1052,6 +1080,8 @@
 
       let LOCAL_PROTOCOLS = ["chrome:", "about:", "resource:", "data:"];
 
+      try {
+      gZenPinnedTabManager.onTabIconChanged(aTab, aIconURL);
       if (
         aIconURL &&
         !aLoadingPrincipal &&
@@ -1062,6 +1092,9 @@
         );
         return;
       }
+      } catch (e) {
+        console.warn(e);
+      }
 
       let browser = this.getBrowserForTab(aTab);
       browser.mIconURL = aIconURL;
@@ -1291,6 +1324,7 @@
       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()) {
@@ -2374,7 +2408,7 @@
 
       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.
@@ -2434,7 +2468,7 @@
       // 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[1].linkedBrowser.browsingContext) this.tabs[1].linkedBrowser.browsingContext.hasSiblings = true;
       } else {
         aTab.linkedBrowser.browsingContext.hasSiblings = this.tabs.length > 1;
       }
@@ -2666,6 +2700,12 @@
         );
       }
 
+      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);
       }
@@ -2735,6 +2775,12 @@
           noInitialLabel,
           skipBackgroundNotify,
         });
+        if (hasZenDefaultUserContextId) {
+          t.setAttribute("zenDefaultUserContextId", "true");
+        }
+        if (zenForcedWorkspaceId !== undefined) {
+          t.setAttribute("zen-workspace-id", zenForcedWorkspaceId);
+        }
         if (insertTab) {
           // insert the tab into the tab container in the correct position
           this._insertTabAtIndex(t, {
@@ -2878,6 +2924,10 @@
         }
       }
 
+      if (typeof window.gZenVerticalTabsManager !== "undefined") {
+        gZenVerticalTabsManager.animateTab(t);
+      }
+
       // Additionally send pinned tab events
       if (pinned) {
         this._notifyPinnedStatus(t);
@@ -3389,6 +3439,23 @@
         ) {
           tabWasReused = true;
           tab = this.selectedTab;
+
+          if (tabData.zenWorkspace) {
+            tab.setAttribute("zen-workspace-id", tabData.zenWorkspace);
+          }
+          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 {
@@ -3402,6 +3469,9 @@
             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.
@@ -3438,6 +3508,21 @@
             preferredRemoteType,
           });
 
+          if (tabData.zenWorkspace) {
+            tab.setAttribute("zen-workspace-id", tabData.zenWorkspace);
+          }
+          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 (select) {
             tabToSelect = tab;
           }
@@ -3491,7 +3576,6 @@
             this.tabContainer._invalidateCachedTabs();
           }
         }
-
         tab.initialize();
       }
 
@@ -4070,6 +4154,10 @@
         return;
       }
 
+      for (let tab of selectedTabs) {
+        gZenPinnedTabManager._removePinnedAttributes(tab, true);
+      }
+
       this.removeTabs(selectedTabs);
     }
 
@@ -4389,6 +4477,13 @@
         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) {
@@ -4417,7 +4512,10 @@
         TelemetryStopwatch.cancel("FX_TAB_CLOSE_TIME_NO_ANIM_MS", aTab);
         return;
       }
-
+      if (aTab.hasAttribute("zen-glance-tab")) {
+        gZenGlanceManager.closeGlance();
+        return;
+      }
       let lockTabSizing =
         !this.tabContainer.verticalMode &&
         !aTab.pinned &&
@@ -4556,14 +4654,14 @@
         !!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;
 
         if (closeWindow) {
           // We've already called beforeunload on all the relevant tabs if we get here,
@@ -5411,10 +5509,10 @@
       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.
@@ -7384,6 +7482,7 @@
             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;
             gBrowser.syncThrobberAnimations(this.mTab);
@@ -8344,7 +8443,7 @@ var TabContextMenu = {
     );
     contextUnpinSelectedTabs.hidden =
       !this.contextTab.pinned || !multiselectionContext;
-
+    gZenPinnedTabManager.updatePinnedTabContextMenu(this.contextTab);
     // Move Tab items
     let contextMoveTabOptions = document.getElementById(
       "context_moveTabOptions"
@@ -8378,7 +8477,7 @@ 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 =
@@ -8607,6 +8706,7 @@ var TabContextMenu = {
     if (this.contextTab.multiselected) {
       gBrowser.removeMultiSelectedTabs();
     } else {
+      gZenPinnedTabManager._removePinnedAttributes(this.contextTab, true);
       gBrowser.removeTab(this.contextTab, { animate: true });
     }
   },