diff --git a/browser/components/tabbrowser/content/tabs.js b/browser/components/tabbrowser/content/tabs.js
index fa96568d366fd3608f9bd583fa793150bd815c8b..5e25d78b04675fbb736192fb0bbcbf6067cbc257 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;
       };
@@ -339,7 +339,7 @@
       // 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;
@@ -388,6 +388,7 @@
             // Reset the "ignored click" flag
             target._ignoredCloseButtonClicks = false;
           }
+          gZenUIManager.saveScrollbarState();
         }
 
         /* Protects from close-tab-button errant doubleclick:
@@ -683,7 +684,7 @@
       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.filter(tab => !tab.hasAttribute("zen-glance-tab")).slice(0, gBrowser._numZenVisibleEssentials);
         let tabsPerRow = 0;
         let position = 0;
         for (let pinnedTab of pinnedTabs) {
@@ -883,6 +884,9 @@
       }
 
       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 &&
@@ -996,6 +1000,14 @@
 
       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);
@@ -1034,8 +1046,8 @@
           }
         } 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
           );
@@ -1114,7 +1126,7 @@
               let postTransitionCleanup = () => {
                 tab.removeAttribute("tabdrop-samewindow");
 
-                this._finishAnimateTabMove();
+              this._finishAnimateTabMove(true);
                 if (dropIndex !== false) {
                   gBrowser.moveTabTo(tab, dropIndex);
                   if (!directionForward) {
@@ -1122,7 +1134,7 @@
                   }
                 }
               };
-              if (gReduceMotion) {
+              if (true || gReduceMotion) {
                 postTransitionCleanup();
               } else {
                 let onTransitionEnd = transitionendEvent => {
@@ -1279,13 +1291,23 @@
         return;
       }
 
-      this._finishMoveTogetherSelectedTabs(draggedTab);
       this._finishAnimateTabMove();
 
+      if (event.ctrlKey && !dt.mozUserCancelled && dt.dropEffect == "none" && !this._isCustomizing) {
+        const moved = gZenViewSplitter.moveTabToSplitView(event, draggedTab);
+        if (moved) {
+          delete draggedTab._dragData;
+          return;
+        }
+      }
+
+      this._finishMoveTogetherSelectedTabs(draggedTab);
+
       if (
         dt.mozUserCancelled ||
         dt.dropEffect != "none" ||
-        this._isCustomizing
+        this._isCustomizing ||
+        draggedTab.pinned
       ) {
         delete draggedTab._dragData;
         return;
@@ -1517,7 +1539,7 @@
     }
 
     get newTabButton() {
-      return this.querySelector("#tabs-newtab-button");
+      return ZenWorkspaces.activeWorkspaceStrip.querySelector("#tabs-newtab-button");
     }
 
     get verticalMode() {
@@ -1537,7 +1559,7 @@
       if (this.#allTabs) {
         return this.#allTabs;
       }
-      let children = Array.from(this.arrowScrollbox.children);
+      let children = ZenWorkspaces.tabboxChildren;
       // remove arrowScrollbox periphery element
       children.pop();
 
@@ -1551,14 +1573,29 @@
       }
 
       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. note: it must be inserted before
+          // the last pinned tab so it can be inserted in the correct order
+          this.#allTabs.splice(Math.min(i + 1, lastPinnedTabIdx), 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 = ZenWorkspaces.tabboxChildren;
       return children.filter(node => node.tagName == "tab-group");
     }
 
@@ -1579,7 +1616,7 @@
      */
     get visibleTabs() {
       if (!this.#visibleTabs) {
-        this.#visibleTabs = this.openTabs.filter(tab => tab.visible);
+        this.#visibleTabs = this.openTabs.filter(tab => tab.visible && !tab.hasAttribute("zen-empty-tab"));
       }
       return this.#visibleTabs;
     }
@@ -1613,10 +1650,8 @@
         return this.#focusableItems;
       }
 
-      let verticalPinnedTabsContainer = document.getElementById(
-        "vertical-pinned-tabs-container"
-      );
-      let children = Array.from(this.arrowScrollbox.children);
+      let verticalPinnedTabsContainer = this.verticalPinnedTabsContainer;
+      let children = ZenWorkspaces.tabboxChildrenWithoutEmpty;
 
       let focusableItems = [];
       for (let child of children) {
@@ -1632,6 +1667,7 @@
       }
 
       this.#focusableItems = [
+        ...document.getElementById("zen-essentials-container").children,
         ...verticalPinnedTabsContainer.children,
         ...focusableItems,
       ];
@@ -1642,6 +1678,7 @@
     _invalidateCachedTabs() {
       this.#allTabs = null;
       this._invalidateCachedVisibleTabs();
+      ZenWorkspaces._allStoredTabs = null;
     }
 
     _invalidateCachedVisibleTabs() {
@@ -1656,8 +1693,8 @@
     #isContainerVerticalPinnedExpanded(tab) {
       return (
         this.verticalMode &&
-        tab.hasAttribute("pinned") &&
-        this.hasAttribute("expanded")
+        (tab.hasAttribute("zen-essential")) &&
+        (this.hasAttribute("expanded") || document.documentElement.hasAttribute("zen-sidebar-expanded"))
       );
     }
 
@@ -1672,7 +1709,7 @@
 
       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);
@@ -1772,7 +1809,7 @@
           // 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"
@@ -1855,7 +1892,7 @@
           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 {
@@ -1867,10 +1904,12 @@
 
     _handleTabSelect(aInstant) {
       let selectedTab = this.selectedItem;
+      if (!selectedTab) return;
       if (this.overflowing) {
         this.arrowScrollbox.ensureElementIsVisible(selectedTab, aInstant);
       }
 
+      gZenCompactModeManager.flashSidebarIfNecessary(aInstant);
       selectedTab._notselectedsinceload = false;
     }
 
@@ -1882,7 +1921,7 @@
         return;
       }
 
-      let tabs = this.visibleTabs;
+      let tabs = this.visibleTabs.filter(tab => !tab.hasAttribute("zen-glance-tab"));
       if (!tabs.length) {
         return;
       }
@@ -1918,7 +1957,7 @@
         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.
@@ -1933,7 +1972,7 @@
         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";
@@ -1999,16 +2038,15 @@
       // 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;
+      if (!ZenWorkspaces._hasInitializedTabsStrip) return;
+      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);
         }
       }
 
@@ -2016,9 +2054,7 @@
     }
 
     _resetVerticalPinnedTabs() {
-      let verticalTabsContainer = document.getElementById(
-        "vertical-pinned-tabs-container"
-      );
+      let verticalTabsContainer = this.verticalPinnedTabsContainer;
 
       if (!verticalTabsContainer.children.length) {
         return;
@@ -2031,8 +2067,8 @@
     }
 
     _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;
 
@@ -2042,6 +2078,7 @@
       if (this.verticalMode) {
         this._updateVerticalPinnedTabs();
       } else if (absPositionHorizontalTabs) {
+        return;
         let layoutData = this._pinnedTabsLayoutCache;
         let uiDensity = document.documentElement.getAttribute("uidensity");
         if (!layoutData || layoutData.uiDensity != uiDensity) {
@@ -2113,7 +2150,7 @@
         return;
       }
 
-      let tabs = this.visibleTabs.slice(0, gBrowser.pinnedTabCount);
+      let tabs = this.visibleTabs.filter(tab => !tab.hasAttribute("zen-glance-tab")).slice(0, gBrowser._numZenVisibleEssentials);
 
       let directionX = screenX > dragData.animLastScreenX;
       let directionY = screenY > dragData.animLastScreenY;
@@ -2296,10 +2333,11 @@
       }
 
       let pinned = draggedTab.pinned;
-      let numPinned = gBrowser.pinnedTabCount;
-      let tabs = this.visibleTabs.slice(
-        pinned ? 0 : numPinned,
-        pinned ? numPinned : undefined
+      let numPinned = gBrowser._numVisiblePinTabs;
+      let essential = draggedTab.hasAttribute("zen-essential");
+      let tabs = this.visibleTabs.filter(tab => !tab.hasAttribute("zen-glance-tab")).slice(
+        pinned ? (essential ? 0 : gBrowser._numZenVisibleEssentials) : numPinned,
+        pinned ? (essential ? gBrowser._numZenVisibleEssentials : ((numPinned - gBrowser._numZenVisibleEssentials) + 1)) : undefined
       );
 
       if (this.#rtlMode) {
@@ -2347,8 +2385,12 @@
         (lastMovingTabScreen + tabSize);
       translate = Math.min(Math.max(translate, firstBound), lastBound);
 
-      for (let tab of movingTabs) {
-        tab.style.transform = `${translateAxis}(${translate}px)`;
+      if (draggedTab.group?.hasAttribute("split-view-group")) {
+        draggedTab.group.style.transform = `${translateAxis}(${translate}px)`;
+      } else {
+        for (let tab of movingTabs) {
+          tab.style.transform = `${translateAxis}(${translate}px)`;
+        }
       }
 
       dragData.translatePos = translate;
@@ -2541,8 +2583,9 @@
       );
     }
 
-    _finishAnimateTabMove() {
-      if (!this.hasAttribute("movingtab")) {
+    _finishAnimateTabMove(always = false) {
+      gZenPinnedTabManager.removeTabContainersDragoverClass();
+      if (!this.hasAttribute("movingtab") && !always) {
         return;
       }
 
@@ -2553,6 +2596,7 @@
         tab.style.transform = "";
         if (tab.group) {
           tab.group.style.removeProperty("--tabgroup-dragover-transform");
+          tab.group.style.transform = "";
         }
         tab.removeAttribute("dragover-createGroup");
       }
@@ -2604,7 +2648,7 @@
           movingTab._moveTogetherSelectedTabsData.newIndex = movingTabNewIndex;
           movingTab._moveTogetherSelectedTabsData.animate = false;
         };
-        if (gReduceMotion) {
+        if (true || gReduceMotion) {
           postTransitionCleanup();
         } else {
           let onTransitionEnd = transitionendEvent => {
@@ -2707,9 +2751,9 @@
       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);
       }
     }
 
@@ -2793,7 +2837,7 @@
     }
 
     _notifyBackgroundTab(aTab) {
-      if (aTab.pinned || !aTab.visible || !this.overflowing) {
+      if (aTab.hasAttribute("zen-essential") || !aTab.visible || !this.overflowing) {
         return;
       }