diff --git a/addon/chrome/content/minit/tablib.js b/addon/chrome/content/minit/tablib.js
index 61d0ae37..7e7355fa 100644
--- a/addon/chrome/content/minit/tablib.js
+++ b/addon/chrome/content/minit/tablib.js
@@ -876,6 +876,7 @@ Tabmix.tablib = {
       return;
     }
 
+    Tabmix.closedObjectsUtils.addSeparatorIfMissing(undoPopup);
     let restoreAllWindows = undoPopup.lastChild;
     restoreAllWindows.setAttribute("value", "-2");
     let clearList = document.createXULElement(undoPopup.__tagName || "menuitem");
@@ -1520,7 +1521,6 @@ Tabmix.tablib = {
       {checkboxLabel2 = "", restoreSession = null} = {}
     ) {
       let warningTitle = "", buttonLabel = "", chkBoxLabel = "", warningText = "";
-      // if (shouldPrompt === 1 || numProtected === 0) {
       if (shouldPrompt === 1) {
         // @ts-expect-error - return types are strings
         [warningTitle, buttonLabel, chkBoxLabel] = gBrowser.tabLocalization.formatValuesSync([
@@ -1529,7 +1529,7 @@ Tabmix.tablib = {
             args: {tabCount: tabsToClose},
           },
           {id: "tabbrowser-confirm-close-tabs-button"},
-          {id: "tabbrowser-confirm-close-tabs-checkbox"},
+          {id: `tabbrowser-${Tabmix.isVersion(1350) ? "ask" : "confirm"}-close-tabs-checkbox`},
         ]);
       } else if (numProtected === 0) {
         // @ts-expect-error - return types are strings
diff --git a/addon/chrome/content/overlay/tabContextMenu.xhtml b/addon/chrome/content/overlay/tabContextMenu.xhtml
index 9460160c..1b92aecb 100644
--- a/addon/chrome/content/overlay/tabContextMenu.xhtml
+++ b/addon/chrome/content/overlay/tabContextMenu.xhtml
@@ -86,9 +86,9 @@
                  tmp_iconic="menu-iconic closedtabs-icon"
                  label="&undoCloseListMenu.label;" accesskey="&undoCloseListMenu.accesskey;">
           <menupopup id="tm-undoCloseList-menu"
-            onpopupshowing="Tabmix.closedObjectsUtils.populateClosedTabsMenu(this.parentNode); event.stopPropagation();"
-            onpopupshown="event.stopPropagation();"
-            onpopuphidden="TabmixAllTabs.hideCommonList(this);"/>
+            onpopupshowing="if (event.target === this) {Tabmix.closedObjectsUtils.populateClosedTabsMenu(this.parentNode); event.stopPropagation();}"
+            onpopupshown="if (event.target === this) event.stopPropagation();"
+            onpopuphidden="if (event.target === this) TabmixAllTabs.hideCommonList(this);"/>
         </menu>
 <!--
         <menuitem id="context_closeTab"/>
diff --git a/addon/chrome/content/session/sessionStore.js b/addon/chrome/content/session/sessionStore.js
index 8e7cd661..0712810a 100644
--- a/addon/chrome/content/session/sessionStore.js
+++ b/addon/chrome/content/session/sessionStore.js
@@ -33,7 +33,7 @@ var TMP_SessionStore = {
     return Promise.resolve(aUndoItem.title);
   },
 
-  // get nsSessionStore active entry data.
+  // get SessionStore active entry data.
   getActiveEntryData: function TMP_ss_getActiveEntryData(aData) {
     let activeIndex = (aData.index || aData.entries.length) - 1;
     if (activeIndex >= aData.entries.length)
@@ -205,7 +205,7 @@ var TMP_SessionStore = {
   afterSwitchThemes: false,
   // we call this only one time on window load
   // and store the value in Tabmix.isWindowAfterSessionRestore
-  // we call this from onContentLoaded before nsSessionStore run its onLoad
+  // we call this from onContentLoaded before SessionStore run its onLoad
   setAfterSessionRestored() {
     let afterSessionRestore;
     if (!Tabmix.isFirstWindow) {
@@ -250,7 +250,7 @@ var TMP_SessionStore = {
   /**
    * @brief           update tab title from user name or bookmark.
    *
-   * @param aTabData  an object value - tabData from nsSessionStore
+   * @param aTabData  an object value - tabData from SessionStore
    *
    * @param aUri      string value - url address
    *
@@ -267,16 +267,16 @@ var TMP_SessionStore = {
   },
 
   /**
-   * @brief           get attribute xultab data
+   * @brief           get custom tab value from SessionStore
    *
-   * @param aTabData  an object value - tabData from nsSessionStore
+   * @param aTabData  an object value - tabData from SessionStore
    *
    * @param attrib    attribute name as string
    *
    * @returns         attribute value as string or empty string.
    */
   _getAttribute: function TMP_ss__getAttribute(aTabData, attrib) {
-    return aTabData.attributes?.[attrib] ?? "";
+    return aTabData.extData?.[attrib] ?? "";
   }
 
 };
@@ -322,7 +322,19 @@ var TMP_ClosedTabs = {
       !Tabmix.isVersion(1170) ?
         "getClosedTabCountForWindow" :
         "getClosedTabCount";
-    return window.__SSi ? TabmixSvc.ss[name](window) : 0;
+    // exclude closed groups from closed windows until Bug 1932941 fixed
+    return window.__SSi ? TabmixSvc.ss[name](window) - this.getClosedTabCountFromClosedGroupInClosedWindows() : 0;
+  },
+
+  getClosedTabCountFromClosedGroupInClosedWindows() {
+    if (!Tabmix.isVersion(1350)) {
+      return 0;
+    }
+    return Object.values(TabmixSvc.SessionStore._closedWindows)
+        .map(winData => winData.closedGroups)
+        .flat()
+        .map(group => group.tabs.length)
+        .reduce((a, b) => a + b, 0);
   },
 
   /**
@@ -330,19 +342,16 @@ var TMP_ClosedTabs = {
    */
   get getClosedTabData() {
     if (window.__SSi) {
-      if (!Tabmix.isVersion(1170)) {
-        return TabmixSvc.ss.getClosedTabDataForWindow(window);
-      }
       return Tabmix.isVersion(1170) ?
         TabmixSvc.ss.getClosedTabData() :
-        TabmixSvc.ss.getClosedTabData(window, false);
+        TabmixSvc.ss.getClosedTabDataForWindow(window);
     }
     return [];
   },
 
   get allClosedTabData() {
     const closedTabsData = this.getClosedTabData;
-    if (Tabmix.isVersion(1190)) {
+    if (Tabmix.isVersion(1190) && !PrivateBrowsingUtils.isWindowPrivate(window)) {
       const restoreClosedTabsFromClosedWindows = Services.prefs.getBoolPref(
         "browser.sessionstore.closedTabsFromClosedWindows"
       );
@@ -376,8 +385,15 @@ var TMP_ClosedTabs = {
     }
 
     const sourceWinData = TabmixSvc.SessionStore._resolveClosedDataSource(source);
-    const closeTabData = sourceWinData._closedTabs.find(tabData => tabData.closedId == index);
-    return closeTabData;
+    if (source.closedWindow) {
+      return sourceWinData._closedTabs.find(tabData => tabData.closedId == index);
+    } else if (Tabmix.isVersion(1350)) {
+      return TabmixSvc.SessionStore._getStateForClosedTabsAndClosedGroupTabs(
+        sourceWinData,
+        index
+      );
+    }
+    return sourceWinData._closedTabs[index];
   },
 
   getUrl: function ct_getUrl(aTabData) {
@@ -403,41 +419,52 @@ var TMP_ClosedTabs = {
     if (!parent.hasAttribute("context")) {
       parent.setAttribute("context", "tm_undocloseContextMenu");
     }
-    const closedTabs = this.getClosedTabData;
+
+    const closedTabsByWindow = this.allClosedTabData.reduce(
+      /** @param {SessionStoreNS.ClosedTabsByWindow} acc */
+      (acc, tabData) => {
+        const {sourceClosedId, sourceWindowId} = tabData;
+        const key = typeof sourceClosedId === "number" ? `closedWindow${sourceClosedId}` : sourceWindowId;
+        if (!acc[key]) {
+          acc[key] = [];
+        }
+        acc[key].push(tabData);
+        return acc;
+      }, {});
+
     const childNodes = parent.childNodes;
     const isSubviewbutton = aPopup.__tagName === "toolbarbutton";
     for (let i = 0; i < childNodes.length - (isAppMenu ? 0 : 1); i++) {
       /** @type {TabmixClosedTabsNS.Menuitem} */ // @ts-expect-error
       let m = childNodes[i];
-      let tabData =
-        i < closedTabs.length ?
-          closedTabs[i] :
-          this.getSingleClosedTabData(this.getSource(m), Number(m.getAttribute("value")));
-      if (tabData && m.hasAttribute("targetURI")) {
-        this.getTitle(tabData, m.getAttribute("targetURI") ?? "").then(title => {
-          m.setAttribute("label", title);
-        });
-      }
-      m.setAttribute("closemenu", this.keepMenuOpen ? "none" : "auto");
-      m.removeAttribute("oncommand");
-      m.addEventListener("command", this, {capture: true, once: true});
-      m.addEventListener("click", this);
-      m.removeEventListener(
-        "click",
-        RecentlyClosedTabsAndWindowsMenuUtils._undoCloseMiddleClick
-      );
-      if (isSubviewbutton) {
-        m.value = i;
-        m.setAttribute("class", "bookmark-item subviewbutton subviewbutton-iconic");
+      if (isSubviewbutton && m.id.startsWith("closed-tabs-tab-group")) {
+        const groupId = m.id.replace("closed-tabs-tab-group-", "");
+        m.nextElementSibling?.setAttribute("data-group-id", groupId);
+        const subview = m.querySelector(".panel-subview-body");
+        subview.setAttribute("context", "tm_undocloseContextMenu");
+        subview.hidePopup = aPopup.hidePopup;
+        this.updateTabGroupItems(m, closedTabsByWindow, isSubviewbutton);
+      } else if (m.tagName === "menu") {
+        this.updateTabGroupItems(m.menupopup, closedTabsByWindow, isSubviewbutton);
+      } else if (
+        !m.previousElementSibling?.id.startsWith("closed-tabs-tab-group") &&
+        m.tagName !== "menuseparator"
+      ) {
+        this.updateMenuItem(m, closedTabsByWindow);
+        if (isSubviewbutton) {
+          m.value = i;
+          m.setAttribute("class", "bookmark-item subviewbutton subviewbutton-iconic");
+        }
       }
     }
 
     if (panel?.__updatingViewAfterDelete) {
-      // we are repopulateing the the list after user removed an item
+      // we are repopulateing the list after user removed an item
       // the menuitem already exist
       return true;
     }
 
+    Tabmix.closedObjectsUtils.addSeparatorIfMissing(aPopup);
     // Reopen All Tabs
     let reopenAllTabs = aPopup.lastChild;
     reopenAllTabs.setAttribute("value", -2);
@@ -455,23 +482,119 @@ var TMP_ClosedTabs = {
     if (isSubviewbutton) {
       reopenAllTabs.classList.add("subviewbutton");
       // "Keep menu open"
-      const mi = addMenu("lockedClosedTabsList", TabmixSvc.getString("undoclosetab.keepOpen.label"), -3);
+      const mi = addMenu({
+        id: "lockedClosedTabsList",
+        label: TabmixSvc.getString("undoclosetab.keepOpen.label"),
+        val: -3,
+      });
       mi.setAttribute("tooltiptext", TabmixSvc.getString("undoclosetab.keepOpen.description"));
       mi.setAttribute("closemenu", "none");
       const image = this.keepMenuOpen ? "chrome://tabmixplus/skin/pin.png" : "";
       Tabmix.setItem(mi, "image", image || null);
     }
     // "Clear Closed Tabs List"
-    addMenu("clearClosedTabsList", TabmixSvc.getString("undoclosetab.clear.label"), -1, "clearClosedTabs");
+    addMenu({
+      id: "clearClosedTabsList",
+      label: TabmixSvc.getString("undoclosetab.clear.label"),
+      val: -1,
+      keyId: "clearClosedTabs",
+    });
 
     return true;
   },
 
-  addMenuItem(popup, isSubviewbutton, id, label, val, keyId) {
-    const m = document.createXULElement(popup.__tagName || "menuitem");
+  updateTabGroupItems(parent, closedTabsByWindow, isSubviewbutton) {
+    const tagName = isSubviewbutton ? "toolbarbutton" : "menuitem";
+    const items = parent.querySelectorAll(tagName);
+    for (const item of Array.from(items).slice(0, -1)) {
+      this.updateMenuItem(item, closedTabsByWindow);
+    }
+    this.addMenuItem(parent, isSubviewbutton, {
+      id: "clearTabGroup",
+      label: "Clear tab group",
+      tagName,
+      command: () => {
+        const {id, ...source} = items.item(0)?.closedGroup ?? {id: ""};
+        TabmixSvc.SessionStore.forgetClosedTabGroup(source, id);
+      },
+    });
+  },
+
+  updateMenuItem(item, closedTabsByWindow) {
+    const index = Number(item.getAttribute("value"));
+
+    const {sourceWindowId, sourceClosedId} = this.getSource(item);
+    const windowKey = typeof sourceClosedId === "number" ? `closedWindow${sourceClosedId}` : sourceWindowId;
+    const closedTabsForWindow = closedTabsByWindow[windowKey];
+    if (closedTabsForWindow) {
+      const tabData = sourceClosedId ?
+        closedTabsForWindow.find(data => data.closedId === index) :
+        closedTabsForWindow.at(index);
+
+      if (tabData && item.hasAttribute("targetURI")) {
+        this.getTitle(tabData, item.getAttribute("targetURI") ?? "").then(title => {
+          item.setAttribute("label", title);
+        });
+      }
+      if (tabData?.state.groupId) {
+        item.closedGroup = {
+          id: tabData.state.groupId,
+          sourceClosedId: tabData.sourceClosedId,
+          sourceWindowId: tabData.sourceWindowId,
+        };
+      }
+    } else {
+      console.log("Tabmix Error: unable to find closed tab data", item,
+        {sourceWindowId, sourceClosedId, windowKey, closedTabsForWindow, closedTabsByWindow});
+    }
+    item.setAttribute("closemenu", this.keepMenuOpen ? "none" : "auto");
+    item.removeAttribute("oncommand");
+    item.addEventListener("command", this, {capture: true, once: true});
+    item.addEventListener("click", this);
+    item.removeEventListener("click", RecentlyClosedTabsAndWindowsMenuUtils._undoCloseMiddleClick);
+  },
+
+  repopulateGroupItems(popup) {
+    this.setPopupWidth(popup);
+    const groupId = popup.parentNode.id.replace("closed-tabs-tab-group-", "");
+    const group = TabmixSvc.SessionStore.getClosedTabGroups().find(g => g.id === groupId);
+    const items = Array.from(popup.querySelectorAll("toolbarbutton"));
+    if (!group) {
+      const panel = popup.parentNode.panelMultiView;
+      panel.goBack();
+      panel.querySelector(`[data-group-id="${groupId}"]`).remove();
+      popup.parentNode.remove();
+      return true;
+    }
+    items.at(-1)?.remove();
+    for (let i = 0; i < items.length - 1; i++) {
+      const item = items[i];
+      const closedTabData = group.tabs[i];
+      if (!item || !closedTabData) {
+        return false;
+      }
+      delete item._tabmix_middleClicked;
+      const {url, title} = TMP_SessionStore.getActiveEntryData(closedTabData.state);
+      if (!url || !title) {
+        return false;
+      }
+      item.setAttribute("targetURI", url);
+      item.setAttribute("label", title);
+      item.addEventListener("command", this, {capture: true, once: true});
+      this.getTitle(closedTabData, item.getAttribute("targetURI") ?? "").then(newTitle => {
+        item.setAttribute("label", newTitle);
+      });
+    }
+    return true;
+  },
+
+  addMenuItem(popup, isSubviewbutton, {id, label, command, val, keyId, tagName}) {
+    const m = document.createXULElement(tagName || popup.__tagName || "menuitem");
     m.setAttribute("id", id);
     m.setAttribute("label", label);
-    m.setAttribute("value", val);
+    if (val) {
+      m.setAttribute("value", val);
+    }
     if (isSubviewbutton) {
       m.setAttribute("class", "subviewbutton");
     } else {
@@ -480,12 +603,17 @@ var TMP_ClosedTabs = {
     if (keyId && document.getElementById("key_tm_" + keyId)) {
       m.setAttribute("key", "key_tm_" + keyId);
     }
-    m.addEventListener("command", this);
+    m.addEventListener("command", command ?? this);
     popup.insertBefore(m, popup.lastChild);
     return m;
   },
 
   handleEvent(event) {
+    if (event.originalTarget._tabmix_middleClicked) {
+      delete event.originalTarget._tabmix_middleClicked;
+      return;
+    }
+
     switch (event.type) {
       case "click":
         this.checkForMiddleClick(event);
@@ -549,7 +677,9 @@ var TMP_ClosedTabs = {
 
     const deleteItem = Tabmix.prefs.getBoolPref("middleclickDelete");
     const where = deleteItem ? "delete" : "tab";
-    this.doCommand("restoreTab", where, aEvent.originalTarget, deleteItem);
+    aEvent.originalTarget._tabmix_middleClicked = true;
+    const keepMenuOpen = deleteItem && aEvent.originalTarget.tagName !== "menuitem";
+    this.doCommand("restoreTab", where, aEvent.originalTarget, keepMenuOpen);
   },
 
   contextMenuOnPopupShowing(popup) {
@@ -566,12 +696,12 @@ var TMP_ClosedTabs = {
     if (!commandData) {
       throw new Error("missing commandData in contextMenuOnCommand");
     }
-    const [command, where] = commandData.split(",");
+    const [command, where = ""] = commandData.split(",");
     const popup = menuItem.parentNode;
     const commands = ["restoreTab", "addBookmarks", "copyTabUrl"];
     /** @type {"restoreTab" | "addBookmarks" | "copyTabUrl"} */ // @ts-expect-error
     const validCommand = commands.find(c => c === command);
-    if (validCommand && where) {
+    if (validCommand) {
       this.doCommand(validCommand, where, popup.triggerNode);
     } else {
       throw new Error(`Unexpected command in contextMenuOnCommand ${command}`);
@@ -583,18 +713,23 @@ var TMP_ClosedTabs = {
     const popup = item.parentNode;
     const index = Number(item.getAttribute("value"));
     const source = this.getSource(item);
+    source.closedGroup = item.closedGroup;
     this[command](source, index, where);
     const rePopulate = (keepMenuOpen || this.keepMenuOpen) && this.count > 0;
     if (rePopulate) {
       if (popup && command == "restoreTab") {
         if (popup.parentNode?.id === "appMenu-library-recentlyClosedTabs") {
           Tabmix.closedObjectsUtils.updateAppmenuView(popup, "Tabs");
+        } else if (popup.parentNode.id.startsWith("closed-tabs-tab-group")) {
+          if (!this.repopulateGroupItems(popup)) {
+            popup.hidePopup();
+          }
         } else {
           this.setPopupWidth(popup);
           Tabmix.closedObjectsUtils.populateClosedTabsMenu(popup.parentNode);
         }
       }
-    } else if (popup.parentNode.tagName === "panelview") {
+    } else if (popup?.parentNode.tagName === "panelview") {
       popup.hidePopup();
     } else if (!this.count || item.getAttribute("closemenu") == "none") {
       closeMenus(popup);
@@ -633,6 +768,8 @@ var TMP_ClosedTabs = {
       case "delete":
         if (source.closedWindow) {
           TabmixSvc.ss.forgetClosedTabById(index, source);
+        } else if (source.closedGroup) {
+          this.getClosedTabAtIndex(source, index);
         } else {
           TabmixSvc.ss.forgetClosedTab(source, index);
         }
@@ -653,6 +790,15 @@ var TMP_ClosedTabs = {
   },
 
   removeAllClosedTabs() {
+    if (Tabmix.isVersion(1350)) {
+      const closedGroups = TabmixSvc.SessionStore.getClosedTabGroups({closedTabsFromClosedWindows: false});
+      for (const group of closedGroups) {
+        const tabData = group.tabs[0];
+        if (tabData) {
+          TabmixSvc.SessionStore.forgetClosedTabGroup(tabData, group.id);
+        }
+      }
+    }
     if (Tabmix.isVersion(1170)) {
       const closedTabsData = this.allClosedTabData;
       for (const {closedId, sourceClosedId, sourceWindowId} of closedTabsData) {
@@ -667,8 +813,8 @@ var TMP_ClosedTabs = {
 
   /**
    * @brief           fetch the data of closed tab, while removing it from the array
-   * @param source    An optional sessionstore id to identify the source window
-   * @param index    a Integer value - 0 or grater index to remove
+   * @param source    optional sessionstore id to identify the source window
+   * @param index     Integer value - 0 or grater index to remove
    * @returns         closed tab data at aIndex.
    */
   getClosedTabAtIndex: function ct_getClosedTabAtIndex(source, index) {
@@ -684,7 +830,32 @@ var TMP_ClosedTabs = {
     if (closedIndex < 0) {
       return null;
     }
-    const closedTab = TabmixSvc.SessionStore.removeClosedTabData(winData, closedTabs, closedIndex);
+
+    if (!Tabmix.isVersion(1350)) {
+      const tabData = TabmixSvc.SessionStore.removeClosedTabData(winData, closedTabs, closedIndex);
+      TabmixSvc.SessionStore._notifyOfClosedObjectsChange();
+      return tabData;
+    }
+
+    const closedTabState = TabmixSvc.SessionStore._getStateForClosedTabsAndClosedGroupTabs(
+      winData,
+      closedIndex
+    );
+    if (!closedTabState) {
+      return null;
+    }
+    const {closedTabSet, closedTabIndex} =
+        TabmixSvc.SessionStore._getClosedTabStateFromUnifiedIndex(winData, closedTabState);
+    const groupIds = closedTabSet?.map(tabData => tabData.state.groupId);
+    const closedTab = TabmixSvc.SessionStore.removeClosedTabData(winData, closedTabSet, closedTabIndex);
+    // temporary fix for bug 1933966
+    for (const groupId of groupIds) {
+      const group = TabmixSvc.SessionStore.getClosedTabGroup(source, groupId);
+      if (group?.tabs.length === 0) {
+        TabmixSvc.SessionStore.forgetClosedTabGroup(source, group.id);
+      }
+    }
+
     TabmixSvc.SessionStore._notifyOfClosedObjectsChange();
     return closedTab;
   },
@@ -778,14 +949,7 @@ var TMP_ClosedTabs = {
       // Predict the remote type to use for the load to avoid unnecessary process
       // switches.
       preferredRemoteType = E10SUtils.DEFAULT_REMOTE_TYPE;
-      let url;
-      if (state.entries?.length) {
-        let activeIndex = (state.index || state.entries.length) - 1;
-        activeIndex = Math.min(activeIndex, state.entries.length - 1);
-        activeIndex = Math.max(activeIndex, 0);
-        // @ts-expect-error entries[activeIndex] exist
-        url = state.entries[activeIndex].url;
-      }
+      const url = this.getUrl(tabData);
       if (url) {
         preferredRemoteType = TabmixSvc.SessionStore.getPreferredRemoteType(
           url,
@@ -1077,6 +1241,18 @@ Tabmix.closedObjectsUtils = {
     menupopup.hasStatusListener = true;
   },
 
+  addSeparatorIfMissing(popup) {
+    if (popup.tagName === "panelview") {
+      return;
+    }
+    const reopenAllmenu = popup.lastChild;
+    if (reopenAllmenu.previousSibling?.tagName !== "menuseparator") {
+      const separator = document.createXULElement("menuseparator");
+      separator.classList.add("bookmark-item", "subviewbutton", "subviewbutton-iconic");
+      popup.insertBefore(separator, reopenAllmenu);
+    }
+  },
+
   populateClosedTabsMenu(undoTabMenu) {
     if (TabmixAllTabs.isAfterCtrlClick(undoTabMenu)) {
       return false;
@@ -1181,7 +1357,12 @@ Tabmix.closedObjectsUtils = {
     while (panel.hasChildNodes()) {
       panel.firstChild.remove();
     }
-    fragment.firstChild.remove();
+    // remove "Restore All Tabs"
+    if (Tabmix.isVersion(1350)) {
+      fragment.lastChild.remove();
+    } else {
+      fragment.firstChild.remove();
+    }
     panel.appendChild(fragment);
     panel.__updatingViewAfterDelete = true;
     if (type === "Tabs") {
diff --git a/addon/chrome/content/tabmix.xhtml b/addon/chrome/content/tabmix.xhtml
index 5473fc90..153670d5 100644
--- a/addon/chrome/content/tabmix.xhtml
+++ b/addon/chrome/content/tabmix.xhtml
@@ -129,8 +129,8 @@
       <menu id="tm-content-undoCloseList" label="&undoCloseListMenu.label;" accesskey="&undoCloseListMenu.accesskey;" tmp_iconic="menu-iconic closedtabs-icon"
          insertbefore="tm-content-after-undoCloseList">
         <menupopup id="tm-content-undoCloseList-menu"
-          onpopupshowing="Tabmix.closedObjectsUtils.populateClosedTabsMenu(this.parentNode);"
-          onpopuphidden="TabmixAllTabs.hideCommonList(this);"/>
+          onpopupshowing="if (event.target === this) Tabmix.closedObjectsUtils.populateClosedTabsMenu(this.parentNode);"
+          onpopuphidden="if (event.target === this) TabmixAllTabs.hideCommonList(this);"/>
       </menu>
       <menu id="tm-autoreload_menu" insertafter="context-sep-navigation"
             labelTab="&autoReloadTab.label;" accesskeyTab="&autoReloadTab.accesskey;"
diff --git a/types/addon.d.ts b/types/addon.d.ts
index a98e6f44..30bd4e74 100644
--- a/types/addon.d.ts
+++ b/types/addon.d.ts
@@ -317,6 +317,11 @@ declare namespace TabmixArrowScrollboxNS {
   }
 }
 
+interface QuerySelectorMap {
+  menuitem: TabmixClosedTabsNS.MenuItemInClosedGroup;
+  toolbarbutton: TabmixClosedTabsNS.MenuItemInClosedGroup;
+}
+
 declare namespace TabmixClosedTabsNS {
   type ClosedTabData = SessionStoreNS.ClosedTabData;
   type ClosedDataSource = SessionStoreNS.ClosedDataSource;
@@ -324,24 +329,30 @@ declare namespace TabmixClosedTabsNS {
 
   type PanelView = ClosedObjectsUtils.CustomPanelView;
   type Popup = ClosedObjectsUtils.PopupElement;
-  type Menuitem = ClosedObjectsUtils.Menuitem;
+  type Menuitem = ClosedObjectsUtils.Menuitem & {closedGroup?: null; _tabmix_middleClicked?: boolean};
   type PopupEvent = Omit<MouseEvent, "target" | "originalTarget"> & {target: Menuitem; originalTarget: Menuitem};
   type ButtonEvent = Omit<MouseEvent, "target"> & {target: HTMLButtonElement};
+  type ClosedGroup = {id: string; sourceClosedId: number; sourceWindowId: string};
+  type MenuItemInClosedGroup = HTMLElement & {closedGroup: ClosedGroup; _tabmix_middleClicked?: boolean};
 
   let _buttonBroadcaster: HTMLElement | null;
   const buttonBroadcaster: HTMLElement;
   function setButtonType(menuOnly: boolean): void;
   function setButtonDisableState(aState?: boolean): void;
   const count: number;
+  function getClosedTabCountFromClosedGroupInClosedWindows(): number;
   const getClosedTabData: ClosedTabData[];
   const allClosedTabData: ClosedTabData[];
-  function getSource(item: Menuitem): ClosedDataSource;
+  function getSource(item: HTMLElement): ClosedDataSource;
   function getSingleClosedTabData(source: ClosedDataSource, index: number): ClosedTabData | undefined;
   function getUrl(aTabData: ClosedTabData): string;
   function getTitle(aTabData: ClosedTabData, aUri: string): Promise<string>;
   let keepMenuOpen: boolean;
   function populateUndoSubmenu(aPopup: PanelView, panel: Popup, isAppMenu?: boolean): boolean;
-  function addMenuItem(popup: PanelView, isSubviewbutton: boolean, id: string, label: string, val: number, keyId?: string): Element;
+  function updateTabGroupItems(menu: Menuitem | Popup, closedTabsByWindow: SessionStoreNS.ClosedTabsByWindow, isSubviewbutton: boolean): void;
+  function updateMenuItem(item: Menuitem | MenuItemInClosedGroup, closedTabs: SessionStoreNS.ClosedTabsByWindow): void;
+  function repopulateGroupItems(popup: Popup): boolean;
+  function addMenuItem(popup: PanelView | Menuitem | Popup, isSubviewbutton: boolean, options: {id: string; label: string; command?: () => void; val?: number; keyId?: string; tagName?: string}): Element;
   function handleEvent(event: PopupEvent): void;
   function handleButtonEvent(event: ButtonEvent): void;
   function restoreCommand(aEvent: PopupEvent): void;
@@ -734,25 +745,21 @@ type UndocloseTabButtonObserver = typeof UndocloseTabButtonObserverNS;
 
 // this namespace is for all SessionStore useage in Tabmix
 declare namespace SessionStoreNS {
-  type ClosedDataSource = Window | {sourceClosedId?: number; sourceWindowId?: string; closedWindow?: boolean; restoreAll?: boolean};
+  type ClosedDataSource = Window | {sourceClosedId?: number; sourceWindowId?: string; closedWindow?: boolean; restoreAll?: boolean; closedGroup?: {id: string} | undefined};
+  type ClosedGroup = Group & {tabs: ClosedTabData[]};
+  type Group = {collapsed: boolean; color: string; id: string; name: string};
   type WindowSource = Window | {sourceWindow: Window; private: boolean; closedTabsFromAllWindows: boolean; closedTabsFromClosedWindows: boolean};
   type TabDataEntry = {url: string; title: string; triggeringPrincipal_base64?: string};
-  type TabData = {
-    attributes?: Record<string, string>;
-    entries: TabDataEntry[];
-    index: number;
-    pinned?: boolean;
-    userContextId?: number;
-    userTypedValue: string;
-    userTypedClear: number;
-    xultab?: string;
-  };
+  type TabData = TabmixNS.TabData;
   type ClosedTabData = {closedId: number; sourceClosedId: number; sourceWindowId: string; pos: number; title: string; state: TabData};
+  type ClosedTabsByWindow = Record<string, ClosedTabData[]>;
   interface WindowState {
     _closedTabs: ClosedTabData[];
     _lastClosedTabGroupCount: number;
     busy?: boolean;
     chromeFlags?: number;
+    closedGroups: ClosedGroup[];
+    groups: Group[];
     height?: number;
     screenX?: number;
     screenY?: number;
@@ -783,6 +790,7 @@ declare namespace SessionStoreNS {
     function duplicateTab(aWindow: Window, aTab: Tab, aDelta?: number, aRestoreImmediately?: boolean, aOptions?: {inBackground?: boolean; index?: number}): void;
     function forgetClosedTab(aSource: ClosedDataSource, aIndex: number): void;
     function forgetClosedTabById(aClosedId: number, aSourceOptions: ClosedDataSource): void;
+    function forgetClosedTabGroup(source: ClosedDataSource, tabGroupId: string): void;
     function forgetClosedWindow(aIndex: number): void;
     function getClosedTabCount(aOptions?: WindowSource): number;
     function getClosedTabCountForWindow(aWindow: Window): number;
@@ -791,6 +799,7 @@ declare namespace SessionStoreNS {
     function getClosedTabData(aWindow: Window, aAsString: boolean): ClosedTabData[];
     function getClosedTabDataForWindow(aWindow: Window): ClosedTabData[];
     function getClosedTabDataFromClosedWindows(): ClosedTabData[];
+    function getClosedTabGroups(aOptions?: Partial<WindowSource>): ClosedGroup[];
     function getClosedWindowCount(): number;
     function getClosedWindowData(): ClosedWindowState[];
     function getCustomTabValue(aTab: Tab, aKey: string): string;
@@ -803,11 +812,16 @@ declare namespace SessionStoreNS {
   }
   export namespace SessionStoreInternal {
     const _windows: Record<SSi, WindowState>;
+    const _closedWindows: ClosedWindowState[];
+    let _closedObjectsChanged: boolean;
     function _isWindowLoaded(aWindow: Window): boolean;
     function _notifyOfClosedObjectsChange(): void;
+    function _getStateForClosedTabsAndClosedGroupTabs(winData: WindowState, aIndex: number): ClosedTabData;
+    function _getClosedTabStateFromUnifiedIndex(winData: WindowState, tabState: ClosedTabData): {closedTabSet: ClosedTabData[]; closedTabIndex: number};
     function _resolveClosedDataSource(source: ClosedDataSource): ClosedWindowState;
     function _resetTabRestoringState(tab: Tab): void;
     function _setWindowStateReady(aWindow: Window): void;
+    function getClosedTabGroup(source: ClosedDataSource, tabGroupId: string | undefined): ClosedGroup | undefined;
     function getPreferredRemoteType(url: string, aWindow: Window, userContextId?: number): string;
     function removeClosedTabData(winData: WindowState, closedTabs: ClosedTabData[], index: number): ClosedTabData;
     function restoreTab(newTab: Tab, state: TabData): void;
diff --git a/types/custom.gecko.dom.d.ts b/types/custom.gecko.dom.d.ts
index a7294043..4644122b 100644
--- a/types/custom.gecko.dom.d.ts
+++ b/types/custom.gecko.dom.d.ts
@@ -54,15 +54,15 @@ declare var MozXULElement: CustomElementConstructorOverride;
 interface QuerySelectorMap {
   '[anonid="useThis"]': HTMLInputElement;
   '[dlgtype="extra1"]': HTMLButtonElement;
-  "[tabmix_context]": NodeList;
+  "[tabmix_context]": HTMLElement;
   ".urlbarView-results": HTMLElement;
-  slot: HTMLElement;
+  "slot": HTMLElement;
 }
 
 interface GetByMap {
-  checkbox: HTMLInputElement;
+  "checkbox": HTMLInputElement;
   "tabmix-tooltip": XULPopupElement;
-  searchbar: CustomSearchbar;
+  "searchbar": CustomSearchbar;
   "tabmix_hideTabbar_menu-container": HTMLTemplateElement;
   "tabmix-closedTabs-container": HTMLTemplateElement;
   "tabmix-closedWindows-container": HTMLTemplateElement;
@@ -89,7 +89,7 @@ interface KnownElements {
 interface HTMLCollectionBase_G<T> {
   readonly length: number;
   item(index: number): T | null;
-  forEach(callbackfn: (value: T | null, key: number, parent: NodeList) => void, thisArg?: any): void;
+  forEach(callbackfn: (value: T, key: number, parent: NodeList) => void, thisArg?: any): void;
   [index: number]: T;
   [Symbol.iterator](): IterableIterator<T | null>;
   entries(): IterableIterator<[number, T | null]>;
@@ -113,7 +113,7 @@ interface ParentNode {
   getElementsByAttribute<K extends keyof GetByMap>(name: K, value: string): HTMLCollection_G<GetByMap[K]>;
   _getElementById<K extends keyof GetByMap | string>(selectors: K): K extends keyof GetByMap ? GetByMap[K] : HTMLElement | null;
   querySelector<K extends keyof QuerySelectorMap | string>(selectors: K): K extends keyof QuerySelectorMap ? QuerySelectorMap[K] : HTMLElement;
-  querySelectorAll<K extends keyof QuerySelectorMap>(selectors: K): QuerySelectorMap[K];
+  querySelectorAll<K extends keyof QuerySelectorMap>(selectors: K): HTMLCollection_G<QuerySelectorMap[K]>;
   querySelectorAll(selectors: string): HTMLCollection_G<HTMLElement>;
 }
 
diff --git a/types/extraTabmixUtils.d.ts b/types/extraTabmixUtils.d.ts
index dd026a04..7071b12e 100644
--- a/types/extraTabmixUtils.d.ts
+++ b/types/extraTabmixUtils.d.ts
@@ -161,12 +161,13 @@ declare namespace TabmixNS {
   type TabData = {
     attributes?: Record<string, string>;
     entries: TabDataEntry[];
+    extData?: Record<string, string>;
+    groupId?: string;
     index: number;
     pinned?: boolean;
     userContextId?: number;
     userTypedValue: string;
     userTypedClear: number;
-    xultab?: string;
   };
 
   const emptyTabTitle: string;
@@ -222,11 +223,15 @@ declare namespace ClosedObjectsUtils {
   interface CustomPanelView extends HTMLElement {
     lastChild: HTMLMenuElement;
     menupopup: PopupElement;
+    panelMultiView: HTMLElement & {
+      goBack(): void;
+    };
   }
 
   type Menuitem = Omit<HTMLMenuElement, "parentNode"> & {
     readonly parentNode: PopupElement;
     readonly triggerNode: Menuitem;
+    menupopup: PopupElement;
     value: number;
   };
 
@@ -251,6 +256,7 @@ declare namespace ClosedObjectsUtils {
   function on_popupshowing(popup: PopupElement): boolean;
   function on_delete(node: Menuitem): void;
   function addHoverListeners(params: CustomPanelView): void;
+  function addSeparatorIfMissing(popup: CustomPanelView): void;
   function populateClosedTabsMenu(undoTabMenu: CustomPanelView): boolean;
   function populateClosedWindowsMenu(undoWindowMenu: CustomPanelView): void;
   function removeObservers(this: typeof ClosedObjectsUtils): void;
diff --git a/types/general.d.ts b/types/general.d.ts
index 88201c5e..ad4b8424 100644
--- a/types/general.d.ts
+++ b/types/general.d.ts
@@ -837,6 +837,7 @@ interface PanelUI {
 interface PrivateBrowsingUtils {
   isBrowserPrivate: (browser: MockedGeckoTypes.ChromeBrowser) => boolean;
   isContentWindowPrivate: (window: Window) => boolean;
+  isWindowPrivate: (window: Window) => boolean;
   permanentPrivateBrowsing: boolean;
 }
 
@@ -947,8 +948,8 @@ declare var PanelMultiView: {
 };
 declare var RecentlyClosedTabsAndWindowsMenuUtils: {
   _undoCloseMiddleClick: (event: MouseEvent) => void;
-  getTabsFragment: (aWindow: Window, aTagName: string, aPrefixRestoreAll?: boolean) => Omit<HTMLElement, "firstChild"> & {firstChild: HTMLElement};
-  getWindowsFragment: (aWindow: Window, aTagName: string, aPrefixRestoreAll?: boolean) => Omit<HTMLElement, "firstChild"> & {firstChild: HTMLElement};
+  getTabsFragment: (aWindow: Window, aTagName: string, aPrefixRestoreAll?: boolean) => Omit<HTMLElement, "firstChild" | "lastChild"> & {firstChild: HTMLElement; lastChild: HTMLElement};
+  getWindowsFragment: (aWindow: Window, aTagName: string, aPrefixRestoreAll?: boolean) => Omit<HTMLElement, "firstChild" | "lastChild"> & {firstChild: HTMLElement; lastChild: HTMLElement};
   onRestoreAllTabsCommand: (event: MouseEvent) => void;
 };
 declare var SessionStartup: {
diff --git a/types/numberInput.d.ts b/types/numberInput.d.ts
index 30f91322..3f2b689b 100644
--- a/types/numberInput.d.ts
+++ b/types/numberInput.d.ts
@@ -22,7 +22,7 @@ declare namespace NumberInput {
 }
 
 interface QuerySelectorMap {
-  "input[type=number]": HTMLNumberInputElement[];
+  "input[type=number]": HTMLNumberInputElement;
 }
 
 interface XULPopupElement {