diff --git a/browser/components/tabbrowser/content/tabs.js b/browser/components/tabbrowser/content/tabs.js
index 8aeb244ffca9f48661805f5b7d860b5896055562..117def8115affccadacfb75da57315ff7eed44ef 100644
--- a/browser/components/tabbrowser/content/tabs.js
+++ b/browser/components/tabbrowser/content/tabs.js
@@ -94,7 +94,7 @@
       };
       this.arrowScrollbox._canScrollToElement = element => {
         if (isTab(element)) {
-          return !element.pinned || !this.hasAttribute("positionpinnedtabs");
+          return !element.hasAttribute("zen-essential") || !this.hasAttribute("positionpinnedtabs");
         }
         return true;
       };
@@ -362,7 +362,7 @@
       // and we're not hitting the scroll buttons.
       if (
         event.button != 0 ||
-        event.target != this.arrowScrollbox ||
+        event.target != document.getElementById("zen-tabs-wrapper") ||
         event.composedTarget.localName == "toolbarbutton"
       ) {
         return;
@@ -411,6 +411,7 @@
             // Reset the "ignored click" flag
             target._ignoredCloseButtonClicks = false;
           }
+          gZenUIManager.saveScrollbarState();
         }
 
         /* Protects from close-tab-button errant doubleclick:
@@ -659,7 +660,7 @@
       if (this.#isContainerVerticalPinnedExpanded(tab)) {
         // In expanded vertical mode, the max number of pinned tabs per row is dynamic
         // Set this before adjusting dragged tab's position
-        let pinnedTabs = this.visibleTabs.slice(0, gBrowser.pinnedTabCount);
+        let pinnedTabs = this.visibleTabs.slice(0, gBrowser._numVisiblePinTabs);
         let tabsPerRow = 0;
         let position = 0;
         for (let pinnedTab of pinnedTabs) {
@@ -859,6 +860,9 @@
       }
 
       let draggedTab = event.dataTransfer.mozGetDataAt(TAB_DROP_TYPE, 0);
+      if (draggedTab && effects === "move") {
+        gZenPinnedTabManager.applyDragoverClass(event, draggedTab);
+      }
       if (
         (effects == "move" || effects == "copy") &&
         this == draggedTab.container &&
@@ -972,6 +976,14 @@
 
       this._tabDropIndicator.hidden = true;
       event.stopPropagation();
+      if (draggedTab && dropEffect == "move") {
+        let moved = gZenPinnedTabManager.moveToAnotherTabContainerIfNecessary(event, movingTabs);
+
+        if (moved) {
+          this._finishMoveTogetherSelectedTabs(draggedTab);
+          return;
+        }
+      }
       if (draggedTab && dropEffect == "copy") {
         // copy the dropped tab (wherever it's from)
         let newIndex = this._getDropIndex(event);
@@ -1010,8 +1022,8 @@
           }
         } else {
           let pinned = draggedTab.pinned;
-          let numPinned = gBrowser.pinnedTabCount;
-          let tabs = this.visibleTabs.slice(
+          let numPinned = gBrowser._numVisiblePinTabs;
+          let tabs = this.visibleTabs.filter(tab => !tab.hasAttribute("zen-glance-tab")).slice(
             pinned ? 0 : numPinned,
             pinned ? numPinned : undefined
           );
@@ -1090,7 +1102,7 @@
               let postTransitionCleanup = () => {
                 tab.removeAttribute("tabdrop-samewindow");
 
-                this._finishAnimateTabMove();
+              this._finishAnimateTabMove(true);
                 if (dropIndex !== false) {
                   gBrowser.moveTabTo(tab, dropIndex);
                   if (!directionForward) {
@@ -1100,7 +1112,7 @@
 
                 gBrowser.syncThrobberAnimations(tab);
               };
-              if (gReduceMotion) {
+            if (gReduceMotion || true) {
                 postTransitionCleanup();
               } else {
                 let onTransitionEnd = transitionendEvent => {
@@ -1263,7 +1275,8 @@
       if (
         dt.mozUserCancelled ||
         dt.dropEffect != "none" ||
-        this._isCustomizing
+        this._isCustomizing ||
+        draggedTab.pinned
       ) {
         delete draggedTab._dragData;
         return;
@@ -1478,7 +1491,7 @@
     }
 
     get newTabButton() {
-      return this.querySelector("#tabs-newtab-button");
+      return ZenWorkspaces.activeWorkspaceStrip.querySelector("#tabs-newtab-button");
     }
 
     get verticalMode() {
@@ -1498,7 +1511,7 @@
       if (this.#allTabs) {
         return this.#allTabs;
       }
-      let children = Array.from(this.arrowScrollbox.children);
+      let children = Array.from(ZenWorkspaces.tabboxChildren);
       // remove arrowScrollbox periphery element
       children.pop();
 
@@ -1512,14 +1525,28 @@
       }
 
       this.#allTabs = [
-        ...this.verticalPinnedTabsContainer.children,
+        ...document.getElementById("zen-essentials-container").children, ...this.verticalPinnedTabsContainer.children,
         ...children,
       ];
+      const lastPinnedTabIdx = gBrowser.pinnedTabCount;
+      for (let i = 0; i < this.#allTabs.length; i++) {
+        // add glance tabs (tabs inside tabs) to the list
+        const glanceTab = this.#allTabs[i].querySelector("tab[zen-glance-tab]");
+        if (glanceTab) {
+          // insert right after the parent tab
+          this.#allTabs.splice(i + 1, 0, glanceTab);
+          i++;
+        } else if (this.#allTabs[i].classList.contains("vertical-pinned-tabs-container-separator")) {
+          // remove the separator from the list
+          this.#allTabs.splice(i, 1);
+          i--;
+        }
+      }
       return this.#allTabs;
     }
 
     get allGroups() {
-      let children = Array.from(this.arrowScrollbox.children);
+      let children = Array.from(ZenWorkspaces.tabboxChildren);
       return children.filter(node => node.tagName == "tab-group");
     }
 
@@ -1574,10 +1601,8 @@
         return this.#focusableItems;
       }
 
-      let verticalPinnedTabsContainer = document.getElementById(
-        "vertical-pinned-tabs-container"
-      );
-      let children = Array.from(this.arrowScrollbox.children);
+      let verticalPinnedTabsContainer = this.verticalPinnedTabsContainer;
+      let children = Array.from(ZenWorkspaces.tabboxChildren);
 
       let focusableItems = [];
       for (let child of children) {
@@ -1593,6 +1618,7 @@
       }
 
       this.#focusableItems = [
+        ...document.getElementById("zen-essentials-container").children,
         ...verticalPinnedTabsContainer.children,
         ...focusableItems,
       ];
@@ -1617,8 +1643,8 @@
     #isContainerVerticalPinnedExpanded(tab) {
       return (
         this.verticalMode &&
-        tab.hasAttribute("pinned") &&
-        this.hasAttribute("expanded")
+        (tab.hasAttribute("zen-essential")) &&
+        (this.hasAttribute("expanded") || document.documentElement.hasAttribute("zen-sidebar-expanded"))
       );
     }
 
@@ -1633,7 +1659,7 @@
 
       if (node == null) {
         // We have a container for non-tab elements at the end of the scrollbox.
-        node = this.arrowScrollbox.lastChild;
+        node = ZenWorkspaces.activeWorkspaceStrip.lastChild;
       }
 
       node.before(tab);
@@ -1733,7 +1759,7 @@
           // There are separate "new tab" buttons for horizontal tabs toolbar, vertical tabs and
           // for when the tab strip is overflowed (which is shared by vertical and horizontal tabs);
           // Attach the long click popup to all of them.
-          const newTab = document.getElementById("new-tab-button");
+          const newTab = ZenWorkspaces.activeWorkspaceStrip.querySelector("#tabs-newtab-button");
           const newTab2 = this.newTabButton;
           const newTabVertical = document.getElementById(
             "vertical-tabs-newtab-button"
@@ -1816,7 +1842,7 @@
           let rect = ele => {
             return window.windowUtils.getBoundsWithoutFlushing(ele);
           };
-          let tab = this.visibleTabs[gBrowser.pinnedTabCount];
+          let tab = this.visibleTabs[gBrowser._numVisiblePinTabs];
           if (tab && rect(tab).width <= this._tabClipWidth) {
             this.setAttribute("closebuttons", "activetab");
           } else {
@@ -1828,10 +1854,12 @@
 
     _handleTabSelect(aInstant) {
       let selectedTab = this.selectedItem;
+      if (!selectedTab) return;
       if (this.overflowing) {
         this.arrowScrollbox.ensureElementIsVisible(selectedTab, aInstant);
       }
 
+      gZenCompactModeManager.flashSidebarIfNecessary(aInstant);
       selectedTab._notselectedsinceload = false;
     }
 
@@ -1843,7 +1871,7 @@
         return;
       }
 
-      let tabs = this.visibleTabs;
+      let tabs = this.visibleTabs.filter(tab => !tab.hasAttribute("zen-glance-tab"));
       if (!tabs.length) {
         return;
       }
@@ -1879,7 +1907,7 @@
         if (isEndTab && !this._hasTabTempMaxWidth) {
           return;
         }
-        let numPinned = gBrowser.pinnedTabCount;
+        let numPinned = gBrowser._numVisiblePinTabs;
         // Force tabs to stay the same width, unless we're closing the last tab,
         // which case we need to let them expand just enough so that the overall
         // tabbar width is the same.
@@ -1894,7 +1922,7 @@
         let tabsToReset = [];
         for (let i = numPinned; i < tabs.length; i++) {
           let tab = tabs[i];
-          tab.style.setProperty("max-width", aTabWidth, "important");
+          //tab.style.setProperty("max-width", aTabWidth, "important");
           if (!isEndTab) {
             // keep tabs the same width
             tab.style.transition = "none";
@@ -1960,16 +1988,15 @@
       // Move pinned tabs to another container when the tabstrip is toggled to vertical
       // and when session restore code calls _positionPinnedTabs; update styling whenever
       // the number of pinned tabs changes.
-      let verticalTabsContainer = document.getElementById(
-        "vertical-pinned-tabs-container"
-      );
+      let verticalTabsContainer = this.verticalPinnedTabsContainer;
       let numPinned = gBrowser.pinnedTabCount;
 
-      if (gBrowser.pinnedTabCount !== verticalTabsContainer.children.length) {
-        let tabs = this.visibleTabs;
+      let count = ZenWorkspaces.makeSurePinTabIsInCorrectPosition();
+      if (gBrowser.pinnedTabCount !== (verticalTabsContainer.children.length - count - 1 + document.getElementById("zen-essentials-container").children.length)) {
+        let tabs = this.allTabs.filter(tab => !tab.hasAttribute("zen-glance-tab"));
         for (let i = 0; i < numPinned; i++) {
           tabs[i].style.marginInlineStart = "";
-          verticalTabsContainer.appendChild(tabs[i]);
+          tabs[i].hasAttribute("zen-essential") ? document.getElementById("zen-essentials-container").appendChild(tabs[i]) : verticalTabsContainer.insertBefore(tabs[i], verticalTabsContainer.lastChild);
         }
       }
 
@@ -1977,9 +2004,7 @@
     }
 
     _resetVerticalPinnedTabs() {
-      let verticalTabsContainer = document.getElementById(
-        "vertical-pinned-tabs-container"
-      );
+      let verticalTabsContainer = this.verticalPinnedTabsContainer;
 
       if (!verticalTabsContainer.children.length) {
         return;
@@ -1992,8 +2017,8 @@
     }
 
     _positionPinnedTabs() {
-      let tabs = this.visibleTabs;
-      let numPinned = gBrowser.pinnedTabCount;
+      let tabs = this.visibleTabs.filter(tab => !tab.hasAttribute("zen-glance-tab"));
+      let numPinned = gBrowser._numVisiblePinTabs;
       let absPositionHorizontalTabs =
         this.overflowing && tabs.length > numPinned && numPinned > 0;
 
@@ -2003,6 +2028,7 @@
       if (this.verticalMode) {
         this._updateVerticalPinnedTabs();
       } else if (absPositionHorizontalTabs) {
+        return;
         let layoutData = this._pinnedTabsLayoutCache;
         let uiDensity = document.documentElement.getAttribute("uidensity");
         if (!layoutData || layoutData.uiDensity != uiDensity) {
@@ -2074,7 +2100,7 @@
         return;
       }
 
-      let tabs = this.visibleTabs.slice(0, gBrowser.pinnedTabCount);
+      let tabs = this.visibleTabs.filter(tab => !tab.hasAttribute("zen-glance-tab")).slice(0, gBrowser._numVisiblePinTabs);
 
       let directionX = screenX > dragData.animLastScreenX;
       let directionY = screenY > dragData.animLastScreenY;
@@ -2257,9 +2283,9 @@
       }
 
       let pinned = draggedTab.pinned;
-      let numPinned = gBrowser.pinnedTabCount;
-      let tabs = this.visibleTabs.slice(
-        pinned ? 0 : numPinned,
+      let numPinned = gBrowser._numVisiblePinTabs;
+      let tabs = this.visibleTabs.filter(tab => !tab.hasAttribute("zen-glance-tab")).slice(
+        pinned ? gBrowser._numZenEssentials : numPinned,
         pinned ? numPinned : undefined
       );
 
@@ -2502,8 +2528,9 @@
       );
     }
 
-    _finishAnimateTabMove() {
-      if (!this.hasAttribute("movingtab")) {
+    _finishAnimateTabMove(always = false) {
+      gZenPinnedTabManager.removeTabContainersDragoverClass();
+      if (!this.hasAttribute("movingtab") && !always) {
         return;
       }
 
@@ -2668,9 +2695,9 @@
       function newIndex(aTab, index) {
         // Don't allow mixing pinned and unpinned tabs.
         if (aTab.pinned) {
-          return Math.min(index, gBrowser.pinnedTabCount - 1);
+          return Math.min(index, gBrowser._numVisiblePinTabs - 1);
         }
-        return Math.max(index, gBrowser.pinnedTabCount);
+        return Math.max(index, gBrowser._numVisiblePinTabs);
       }
     }
 
@@ -2754,7 +2781,7 @@
     }
 
     _notifyBackgroundTab(aTab) {
-      if (aTab.pinned || !aTab.visible || !this.overflowing) {
+      if (aTab.hasAttribute("zen-essential") || !aTab.visible || !this.overflowing) {
         return;
       }
 
@@ -2772,12 +2799,14 @@
               selectedTab = {
                 left: selectedTab.left,
                 right: selectedTab.right,
+                top: selectedTab.top,
+                bottom: selectedTab.bottom,
               };
             }
             return [
               this._lastTabToScrollIntoView,
               this.arrowScrollbox.scrollClientRect,
-              { left: lastTabRect.left, right: lastTabRect.right },
+              lastTabRect,
               selectedTab,
             ];
           })
@@ -2794,8 +2823,11 @@
             delete this._lastTabToScrollIntoView;
             // Is the new tab already completely visible?
             if (
-              scrollRect.left <= tabRect.left &&
-              tabRect.right <= scrollRect.right
+              this.verticalMode
+                ? scrollRect.top <= tabRect.top &&
+                  tabRect.bottom <= scrollRect.bottom
+                : scrollRect.left <= tabRect.left &&
+                  tabRect.right <= scrollRect.right
             ) {
               return;
             }
@@ -2803,21 +2835,29 @@
             if (this.arrowScrollbox.smoothScroll) {
               // Can we make both the new tab and the selected tab completely visible?
               if (
-                !selectedRect ||
-                Math.max(
-                  tabRect.right - selectedRect.left,
-                  selectedRect.right - tabRect.left
-                ) <= scrollRect.width
+                !selectedRect || (this.verticalMode
+                  ? Math.max(
+                      tabRect.bottom - selectedRect.top,
+                      selectedRect.bottom - tabRect.top
+                    ) <= scrollRect.height
+                  : Math.max(
+                      tabRect.right - selectedRect.left,
+                      selectedRect.right - tabRect.left
+                    ) <= scrollRect.width)
               ) {
                 this.arrowScrollbox.ensureElementIsVisible(tabToScrollIntoView);
                 return;
               }
 
-              this.arrowScrollbox.scrollByPixels(
-                this.#rtlMode
-                  ? selectedRect.right - scrollRect.right
-                  : selectedRect.left - scrollRect.left
-              );
+              let scrollPixels;
+              if (this.verticalMode) {
+                scrollPixels = tabRect.top - selectedRect.top;
+              } else if (this.#rtlMode) {
+                scrollPixels = selectedRect.right - scrollRect.right;
+              } else {
+                scrollPixels = selectedRect.left - scrollRect.left;
+              }
+              this.arrowScrollbox.scrollByPixels(scrollPixels);
             }
 
             if (!this._animateElement.hasAttribute("highlight")) {