diff --git a/calendar/test/mozmill/testTodayPane.js b/calendar/test/mozmill/testTodayPane.js
index a6d871c2b9..412d4e04c4 100755
--- a/calendar/test/mozmill/testTodayPane.js
+++ b/calendar/test/mozmill/testTodayPane.js
@@ -130,7 +130,7 @@ function testTodayPane() {
     // go to mail tab
     controller.click(lookup(`
         /id("messengerWindow")/id("navigation-toolbox")/id("tabs-toolbar")/
-        id("tabcontainer")/{"first-tab":"true","type":"folder"}/
+        id("tabmail-tabs")/{"first-tab":"true","type":"folder"}/
         anon({"class":"tab-stack"})/{"class":"tab-background"}/
         {"class":"tab-line"}
     `));
diff --git a/mail/base/content/messenger.xul b/mail/base/content/messenger.xul
index ce3a4d764f..e3b1cfb74f 100644
--- a/mail/base/content/messenger.xul
+++ b/mail/base/content/messenger.xul
@@ -240,9 +240,9 @@
   <toolbox id="navigation-toolbox" class="toolbox-top">
 
     <toolbar id="tabs-toolbar" class="toolbar-primary">
-
+      <!-- class tabmail-tabs is unused and only maintained for add-ons. -->
       <tabs flex="1"
-            id="tabcontainer"
+            id="tabmail-tabs"
             align="end"
             setfocus="false"
             onclick="document.getElementById('tabmail').onTabClick(event);"
@@ -275,7 +275,7 @@
                      tooltiptext="&listAllTabs.label;">
         <menupopup class="tabs-alltabs-popup"
                    id="alltabs-popup" position="after_end"
-                   tabcontainer="tabcontainer"/>
+                   tabcontainer="tabmail-tabs"/>
       </toolbarbutton>
 #ifdef CAN_DRAW_IN_TITLEBAR
       <hbox class="titlebar-placeholder" type="caption-buttons"
@@ -302,7 +302,7 @@
          of tabmail is OK though).  This will break Ctrl-tab switching because
          the XBL binding will choke when it finds a child of tabmail that is
          not a tabpanels node. -->
-    <tabmail id="tabmail" flex="1" panelcontainer="tabpanelcontainer" tabcontainer="tabcontainer">
+    <tabmail id="tabmail" flex="1" panelcontainer="tabpanelcontainer" tabcontainer="tabmail-tabs">
       <tabpanels id="tabpanelcontainer" flex="1" class="plain" selectedIndex="0">
 
         <!-- mailContent is the container used for the "wide" layout. Normally,
diff --git a/mail/base/content/tabmail.css b/mail/base/content/tabmail.css
index 23add8ae5b..6b73f3ea55 100644
--- a/mail/base/content/tabmail.css
+++ b/mail/base/content/tabmail.css
@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-.tabmail-tabs {
+#tabmail-tabs {
   -moz-binding: url("chrome://messenger/content/tabmail.xml#tabmail-tabs");
 }
 
@@ -46,17 +46,17 @@
   display: none;
 }
 
-.tabmail-tabs > .tabmail-tab[first-tab] > .tab-stack > .tab-content >
+#tabmail-tabs > .tabmail-tab[first-tab] > .tab-stack > .tab-content >
 .tab-close-button {
   visibility: collapse;
 }
 
-.tabmail-tabs:not([closebuttons="noclose"]):not([closebuttons="closeatend"]) >
+#tabmail-tabs:not([closebuttons="noclose"]):not([closebuttons="closeatend"]) >
 .tabmail-tab[selected="true"]:not(:only-child) > .tab-stack > .tab-content > .tab-close-button {
   display: -moz-box;
 }
 
-.tabmail-tabs[closebuttons="alltabs"] > .tabmail-tab:not(:only-child) >
+#tabmail-tabs[closebuttons="alltabs"] > .tabmail-tab:not(:only-child) >
 .tab-stack > .tab-content > .tab-close-button {
   display: -moz-box;
 }
diff --git a/mail/test/mozmill/tabmail/test-tabmail-customize.js b/mail/test/mozmill/tabmail/test-tabmail-customize.js
index 0af3b3a33c..ccc3c83659 100644
--- a/mail/test/mozmill/tabmail/test-tabmail-customize.js
+++ b/mail/test/mozmill/tabmail/test-tabmail-customize.js
@@ -42,7 +42,7 @@ function test_open_context_menu() {
   assert_not_equals(contextPopup.state, "open");
 
   // Right click on the tab bar
-  mc.rightClick(mc.eid("tabcontainer"));
+  mc.rightClick(mc.eid("tabmail-tabs"));
 
   // Ensure that the popup opened
   wait_for_popup_to_open(contextPopup);
@@ -58,7 +58,7 @@ function test_redirects_toolbarbutton_drops() {
   // Restore the default buttons to get defined starting conditions.
   gCDHelper.restoreDefaultButtons(mc);
 
-  let tabbar = mc.e("tabcontainer");
+  let tabbar = mc.e("tabmail-tabs");
   let toolbar = mc.e("tabbar-toolbar");
 
   // First, let's open up the customize toolbar window.
diff --git a/mail/themes/osx/mail/tabmail.css b/mail/themes/osx/mail/tabmail.css
index 642d2d12e9..defd077a13 100644
--- a/mail/themes/osx/mail/tabmail.css
+++ b/mail/themes/osx/mail/tabmail.css
@@ -69,7 +69,7 @@
   box-shadow: var(--focus-ring-box-shadow);
 }
 
-.tabmail-tabs {
+#tabmail-tabs {
   border: none;
   -moz-box-pack: center;
   -moz-box-align: center;
diff --git a/mail/themes/shared/mail/tabmail.css b/mail/themes/shared/mail/tabmail.css
index e1a263123c..3dbcb53a70 100644
--- a/mail/themes/shared/mail/tabmail.css
+++ b/mail/themes/shared/mail/tabmail.css
@@ -118,7 +118,7 @@
 }
 
 :root:not([tabsintitlebar]) .tab-background,
-#mail-toolbar-menubar2[toolbarname]:not([autohide=true]) ~ #tabs-toolbar > .tabmail-tabs >
+#mail-toolbar-menubar2[toolbarname]:not([autohide=true]) ~ #tabs-toolbar > #tabmail-tabs >
   .tabmail-tab > .tab-stack > .tab-background {
   border-top-style: solid;
 }
@@ -156,7 +156,7 @@
   background-color: rgba(0,0,0,.1);
 }
 
-#tabs-toolbar[brighttext] > .tabmail-tabs > .tabmail-tab:hover > .tab-stack >
+#tabs-toolbar[brighttext] > #tabmail-tabs > .tabmail-tab:hover > .tab-stack >
   .tab-background:not([selected=true]) {
   background-color: rgba(255,255,255,.1);
 }
@@ -174,7 +174,7 @@
   transform: none;
 }
 
-#tabs-toolbar[brighttext] > .tabmail-tabs > .tabmail-tab:hover > .tab-stack >
+#tabs-toolbar[brighttext] > #tabmail-tabs > .tabmail-tab:hover > .tab-stack >
   .tab-background > .tab-line:not([selected=true]) {
   background-color: rgba(255,255,255,.2);
 }
@@ -215,8 +215,8 @@
 .tabmail-tab:not([selected=true]):last-child:hover::after,
 .tabmail-tab:not([selected]) + .tabmail-tab:not([selected]):hover::before,
 .tabmail-tab:not([selected]):hover + .tabmail-tab:not([selected])::before,
-:root[tabsintitlebar] #mail-toolbar-menubar2[autohide=true] ~ #tabs-toolbar > .tabmail-tabs > .tabmail-tab::after,
-:root[tabsintitlebar] #mail-toolbar-menubar2[autohide=true] ~ #tabs-toolbar > .tabmail-tabs > .tabmail-tab::before {
+:root[tabsintitlebar] #mail-toolbar-menubar2[autohide=true] ~ #tabs-toolbar > #tabmail-tabs > .tabmail-tab::after,
+:root[tabsintitlebar] #mail-toolbar-menubar2[autohide=true] ~ #tabs-toolbar > #tabmail-tabs > .tabmail-tab::before {
   margin-top: var(--tabs-top-border-width);
   margin-bottom: var(--tab-toolbar-overlap);
 }
diff --git a/mail/themes/windows/mail/primaryToolbar.css b/mail/themes/windows/mail/primaryToolbar.css
index 592c0e25d7..0aa7999007 100644
--- a/mail/themes/windows/mail/primaryToolbar.css
+++ b/mail/themes/windows/mail/primaryToolbar.css
@@ -61,7 +61,7 @@
  */
 @media (-moz-windows-classic) {
   #messengerWindow[tabsintitlebar]:not([sizemode=fullscreen])
-  .tabmail-tabs:not(:-moz-lwtheme) {
+  #tabmail-tabs:not(:-moz-lwtheme) {
     position: relative;
     z-index: 2;
   }