diff --git a/browser/components/tabbrowser/content/tabbrowser.js b/browser/components/tabbrowser/content/tabbrowser.js
index ef857bd81f2cd7c163ecc74ac1cf81a0b63ce838..807eb0c493f15643412b05d8dad81d36d7470155 100644
--- a/browser/components/tabbrowser/content/tabbrowser.js
+++ b/browser/components/tabbrowser/content/tabbrowser.js
@@ -452,11 +452,26 @@
       return duplicateTabs;
     },
 
+    get _numVisiblePinTabs() {
+      let i = 0;
+      for (let tab of this.tabs) {
+        if (!tab.pinned) {
+          break;
+        }
+        if (!tab.hidden) {
+          i++;
+        }
+      }
+      return i;
+    },
+
     get _numPinnedTabs() {
-      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;
     },
@@ -2704,6 +2719,11 @@
         );
       }
 
+      let hasZenDefaultUserContextId = false;
+      if (typeof ZenWorkspaces !== "undefined") {
+        [userContextId, hasZenDefaultUserContextId] = ZenWorkspaces.getContextIdIfNeeded(userContextId);
+      }
+
       if (!UserInteraction.running("browser.tabs.opening", window)) {
         UserInteraction.start("browser.tabs.opening", "initting", window);
       }
@@ -2771,6 +2791,9 @@
           noInitialLabel,
           skipBackgroundNotify,
         });
+        if (hasZenDefaultUserContextId) {
+          t.setAttribute("zenDefaultUserContextId", "true");
+        }
         if (insertTab) {
           // insert the tab into the tab container in the correct position
           this._insertTabAtIndex(t, {
@@ -3248,6 +3271,14 @@
         ) {
           tabWasReused = true;
           tab = this.selectedTab;
+
+          if (tabData.zenWorkspace) {
+            tab.setAttribute("zen-workspace-id", tabData.zenWorkspace);
+          }
+          if (tabData.zenDefaultUserContextId) {
+            tab.setAttribute("zenDefaultUserContextId", "true");
+          }
+
           if (!tabData.pinned) {
             this.unpinTab(tab);
           } else {
@@ -3297,6 +3328,13 @@
             preferredRemoteType,
           });
 
+          if (tabData.zenWorkspace) {
+            tab.setAttribute("zen-workspace-id", tabData.zenWorkspace);
+          }
+          if (tabData.zenDefaultUserContextId) {
+            tab.setAttribute("zenDefaultUserContextId", "true");
+          }
+
           if (select) {
             tabToSelect = tab;
           }
@@ -4184,6 +4222,7 @@
         isLastTab ||
         aTab.pinned ||
         aTab.hidden ||
+        true ||
         this._removingTabs.size >
           3 /* don't want lots of concurrent animations */ ||
         !aTab.hasAttribute(
@@ -5117,10 +5156,10 @@
       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.