--- a/browser/components/tabbrowser/content/tabs.js
+++ b/browser/components/tabbrowser/content/tabs.js
@@ -587,17 +587,17 @@
       // Set the cursor to an arrow during tab drags.
       dt.mozCursor = "default";
 
       // Set the tab as the source of the drag, which ensures we have a stable
       // node to deliver the `dragend` event.  See bug 1345473.
       dt.addElement(tab);
 
       if (tab.multiselected) {
-        this._groupSelectedTabs(tab);
+        this.#moveTogetherSelectedTabs(tab);
       }
 
       // Create a canvas to which we capture the current tab.
       // Until canvas is HiDPI-aware (bug 780362), we need to scale the desired
       // canvas size (in CSS pixels) to the window's backing resolution in order
       // to get a full-resolution drag image for use on HiDPI displays.
       let scale = window.devicePixelRatio;
       let canvas = this._dndCanvas;
@@ -736,25 +736,25 @@
       let draggedTab = event.dataTransfer.mozGetDataAt(TAB_DROP_TYPE, 0);
       if (
         (effects == "move" || effects == "copy") &&
         this == draggedTab.container &&
         !draggedTab._dragData.fromTabList
       ) {
         ind.hidden = true;
 
-        if (!this._isGroupTabsAnimationOver()) {
-          // Wait for grouping tabs animation to finish
+        if (this.#isAnimatingMoveTogetherSelectedTabs()) {
+          // Wait for moving selected tabs together animation to finish.
           return;
         }
-        this._finishGroupSelectedTabs(draggedTab);
+        this._finishMoveTogetherSelectedTabs(draggedTab);
 
         if (effects == "move") {
           // Pinned tabs in expanded vertical mode are on a grid format and require
-          // different logic to drag and drop
+          // different logic to drag and drop.
           if (this.#isContainerVerticalPinnedExpanded(draggedTab)) {
             this.#animateExpandedPinnedTabMove(event);
             return;
           }
           this._animateTabMove(event);
           return;
         }
       }
@@ -836,17 +836,17 @@
       if (dt.mozTypesAt(0)[0] == TAB_DROP_TYPE) {
         // tab copy or move
         draggedTab = dt.mozGetDataAt(TAB_DROP_TYPE, 0);
         // not our drop then
         if (!draggedTab) {
           return;
         }
         movingTabs = draggedTab._dragData.movingTabs;
-        draggedTab.container._finishGroupSelectedTabs(draggedTab);
+        draggedTab.container._finishMoveTogetherSelectedTabs(draggedTab);
       }
 
       this._tabDropIndicator.hidden = true;
       event.stopPropagation();
       if (draggedTab && dropEffect == "copy") {
         // copy the dropped tab (wherever it's from)
         let newIndex = this._getDropIndex(event);
         let draggedTabCopy;
@@ -1063,17 +1063,17 @@
 
       // Prevent this code from running if a tabdrop animation is
       // running since calling _finishAnimateTabMove would clear
       // any CSS transition that is running.
       if (draggedTab.hasAttribute("tabdrop-samewindow")) {
         return;
       }
 
-      this._finishGroupSelectedTabs(draggedTab);
+      this._finishMoveTogetherSelectedTabs(draggedTab);
       this._finishAnimateTabMove();
 
       if (
         dt.mozUserCancelled ||
         dt.dropEffect != "none" ||
         this._isCustomizing
       ) {
         delete draggedTab._dragData;
@@ -2153,25 +2153,24 @@
       this.removeAttribute("movingtab-createGroup");
       this.#setDragOverGroupColor(null);
       gNavToolbox.removeAttribute("movingtab");
 
       this._handleTabSelect();
     }
 
     /**
-     * Regroup all selected tabs around the
-     * tab in param
+     * Move together all selected tabs around the tab in param.
      */
-    _groupSelectedTabs(tab) {
+    #moveTogetherSelectedTabs(tab) {
       let draggedTabPos = tab._tPos;
       let selectedTabs = gBrowser.selectedTabs;
       let animate = !gReduceMotion;
 
-      tab.groupingTabsData = {
+      tab._moveTogetherSelectedTabsData = {
         finished: !animate,
       };
 
       let addAnimationData = (
         movingTab,
         movingTabNewIndex,
         isBeforeSelectedTab = true
       ) => {
@@ -2184,24 +2183,24 @@
         }
 
         let movingTabSize =
           movingTab.getBoundingClientRect()[
             this.verticalMode ? "height" : "width"
           ];
         let shift = (movingTabNewIndex - movingTabOldIndex) * movingTabSize;
 
-        movingTab.groupingTabsData.animate = true;
-        movingTab.toggleAttribute("tab-grouping", true);
+        movingTab._moveTogetherSelectedTabsData.animate = true;
+        movingTab.toggleAttribute("multiselected-move-together", true);
 
-        movingTab.groupingTabsData.translatePos = shift;
+        movingTab._moveTogetherSelectedTabsData.translatePos = shift;
 
         let postTransitionCleanup = () => {
-          movingTab.groupingTabsData.newIndex = movingTabNewIndex;
-          movingTab.groupingTabsData.animate = false;
+          movingTab._moveTogetherSelectedTabsData.newIndex = movingTabNewIndex;
+          movingTab._moveTogetherSelectedTabsData.animate = false;
         };
         if (gReduceMotion) {
           postTransitionCleanup();
         } else {
           let onTransitionEnd = transitionendEvent => {
             if (
               transitionendEvent.propertyName != "transform" ||
               transitionendEvent.originalTarget != movingTab
@@ -2232,40 +2231,39 @@
           }
 
           if (middleTab.multiselected) {
             // Skip because this selected tab should
             // be shifted towards the dragged Tab.
             continue;
           }
 
-          if (
-            !middleTab.groupingTabsData ||
-            !middleTab.groupingTabsData.translatePos
-          ) {
-            middleTab.groupingTabsData = { translatePos: 0 };
+          if (!middleTab._moveTogetherSelectedTabsData?.translatePos) {
+            middleTab._moveTogetherSelectedTabsData = { translatePos: 0 };
           }
           if (isBeforeSelectedTab) {
-            middleTab.groupingTabsData.translatePos -= movingTabSize;
+            middleTab._moveTogetherSelectedTabsData.translatePos -=
+              movingTabSize;
           } else {
-            middleTab.groupingTabsData.translatePos += movingTabSize;
+            middleTab._moveTogetherSelectedTabsData.translatePos +=
+              movingTabSize;
           }
 
-          middleTab.toggleAttribute("tab-grouping", true);
+          middleTab.toggleAttribute("multiselected-move-together", true);
         }
       };
 
       // Animate left or top selected tabs
       let insertAtPos = draggedTabPos - 1;
       for (let i = selectedTabs.indexOf(tab) - 1; i > -1; i--) {
         let movingTab = selectedTabs[i];
         insertAtPos = newIndex(movingTab, insertAtPos);
 
         if (animate) {
-          movingTab.groupingTabsData = {};
+          movingTab._moveTogetherSelectedTabsData = {};
           addAnimationData(movingTab, insertAtPos, true);
         } else {
           gBrowser.moveTabTo(movingTab, insertAtPos);
         }
         insertAtPos--;
       }
 
       // Animate right or bottom selected tabs
@@ -2274,84 +2272,94 @@
         let i = selectedTabs.indexOf(tab) + 1;
         i < selectedTabs.length;
         i++
       ) {
         let movingTab = selectedTabs[i];
         insertAtPos = newIndex(movingTab, insertAtPos);
 
         if (animate) {
-          movingTab.groupingTabsData = {};
+          movingTab._moveTogetherSelectedTabsData = {};
           addAnimationData(movingTab, insertAtPos, false);
         } else {
           gBrowser.moveTabTo(movingTab, insertAtPos);
         }
         insertAtPos++;
       }
 
       // Slide the relevant tabs to their new position.
       for (let t of this.visibleTabs) {
-        if (t.groupingTabsData && t.groupingTabsData.translatePos) {
+        if (t._moveTogetherSelectedTabsData?.translatePos) {
           let translatePos =
-            (this.#rtlMode ? -1 : 1) * t.groupingTabsData.translatePos;
+            (this.#rtlMode ? -1 : 1) *
+            t._moveTogetherSelectedTabsData.translatePos;
           t.style.transform = `translate${
             this.verticalMode ? "Y" : "X"
           }(${translatePos}px)`;
         }
       }
 
       function newIndex(aTab, index) {
         // Don't allow mixing pinned and unpinned tabs.
         if (aTab.pinned) {
           return Math.min(index, gBrowser.pinnedTabCount - 1);
         }
         return Math.max(index, gBrowser.pinnedTabCount);
       }
     }
 
-    _finishGroupSelectedTabs(tab) {
-      if (!tab.groupingTabsData || tab.groupingTabsData.finished) {
+    _finishMoveTogetherSelectedTabs(tab) {
+      if (
+        !tab._moveTogetherSelectedTabsData ||
+        tab._moveTogetherSelectedTabsData.finished
+      ) {
         return;
       }
 
-      tab.groupingTabsData.finished = true;
+      tab._moveTogetherSelectedTabsData.finished = true;
 
       let selectedTabs = gBrowser.selectedTabs;
       let tabIndex = selectedTabs.indexOf(tab);
 
       // Moving left or top tabs
       for (let i = tabIndex - 1; i > -1; i--) {
         let movingTab = selectedTabs[i];
-        if (movingTab.groupingTabsData.newIndex) {
-          gBrowser.moveTabTo(movingTab, movingTab.groupingTabsData.newIndex);
+        if (movingTab._moveTogetherSelectedTabsData.newIndex) {
+          gBrowser.moveTabTo(
+            movingTab,
+            movingTab._moveTogetherSelectedTabsData.newIndex
+          );
         }
       }
 
       // Moving right or bottom tabs
       for (let i = tabIndex + 1; i < selectedTabs.length; i++) {
         let movingTab = selectedTabs[i];
-        if (movingTab.groupingTabsData.newIndex) {
-          gBrowser.moveTabTo(movingTab, movingTab.groupingTabsData.newIndex);
+        if (movingTab._moveTogetherSelectedTabsData.newIndex) {
+          gBrowser.moveTabTo(
+            movingTab,
+            movingTab._moveTogetherSelectedTabsData.newIndex
+          );
         }
       }
 
       for (let t of this.visibleTabs) {
         t.style.transform = "";
-        t.removeAttribute("tab-grouping");
-        delete t.groupingTabsData;
+        t.removeAttribute("multiselected-move-together");
+        delete t._moveTogetherSelectedTabsData;
       }
     }
 
-    _isGroupTabsAnimationOver() {
+    #isAnimatingMoveTogetherSelectedTabs() {
       for (let tab of gBrowser.selectedTabs) {
-        if (tab.groupingTabsData && tab.groupingTabsData.animate) {
-          return false;
+        if (tab._moveTogetherSelectedTabsData?.animate) {
+          return true;
         }
       }
-      return true;
+      return false;
     }
 
     handleEvent(aEvent) {
       switch (aEvent.type) {
         case "mouseout":
           // If the "related target" (the node to which the pointer went) is not
           // a child of the current document, the mouse just left the window.
           let relatedTarget = aEvent.relatedTarget;