diff --git a/browser/components/tabbrowser/content/tabbrowser.js b/browser/components/tabbrowser/content/tabbrowser.js
index 94b62b6f06d2..813cbcf65277 100644
--- a/browser/components/tabbrowser/content/tabbrowser.js
+++ b/browser/components/tabbrowser/content/tabbrowser.js
@@ -5865,7 +5865,7 @@
               nextTab.group.after(selectedTab);
             } else {
               // Enter first position of tab group.
-              nextTab.group.prepend(selectedTab);
+              nextTab.group.insertBefore(selectedTab, nextTab);
             }
           } else if (selectedTab.group != nextTab.group) {
             // Standalone tab after tab group.
@@ -5874,6 +5874,10 @@
             nextTab.after(selectedTab);
           }
         });
+      } else if (selectedTab.group) {
+        // selectedTab is the last tab and is grouped.
+        // remove it from its group.
+        selectedTab.group.after(selectedTab);
       }
     }
 
@@ -5902,6 +5906,10 @@
             previousTab.before(selectedTab);
           }
         });
+      } else if (selectedTab.group) {
+        // selectedTab is the first tab and is grouped.
+        // remove it from its group.
+        selectedTab.group.before(selectedTab);
       }
     }
 
diff --git a/browser/components/tabbrowser/test/browser/tabs/browser_tab_move_active_tab.js b/browser/components/tabbrowser/test/browser/tabs/browser_tab_move_active_tab.js
index eeff3c2225cc..f93ac098a95e 100644
--- a/browser/components/tabbrowser/test/browser/tabs/browser_tab_move_active_tab.js
+++ b/browser/components/tabbrowser/test/browser/tabs/browser_tab_move_active_tab.js
@@ -144,8 +144,6 @@ add_task(async function test_moveTabForwardTabGroups() {
   let tab2 = BrowserTestUtils.addTab(gBrowser, "about:blank");
   let tab3 = BrowserTestUtils.addTab(gBrowser, "about:blank");
   let tab4 = BrowserTestUtils.addTab(gBrowser, "about:blank");
-  let tab5 = BrowserTestUtils.addTab(gBrowser, "about:blank");
-  let tab6 = BrowserTestUtils.addTab(gBrowser, "about:blank");
   let group1 = gBrowser.addTabGroup([tab3], { insertBefore: tab3 });
   let group2 = gBrowser.addTabGroup([tab4], { insertBefore: tab4 });
   gBrowser.selectedTab = tab1;
@@ -156,8 +154,6 @@ add_task(async function test_moveTabForwardTabGroups() {
     [tab2, 2],
     [tab3, 3],
     [tab4, 4],
-    [tab5, 5],
-    [tab6, 6],
   ]);
   Assert.ok(!tab1.group, "tab1 should not be in a tab group");
 
@@ -168,8 +164,6 @@ add_task(async function test_moveTabForwardTabGroups() {
     [tab2, 1],
     [tab3, 3],
     [tab4, 4],
-    [tab5, 5],
-    [tab6, 6],
   ]);
   Assert.ok(!tab1.group, "tab1 should not be in a tab group");
 
@@ -180,10 +174,13 @@ add_task(async function test_moveTabForwardTabGroups() {
     [tab2, 1],
     [tab3, 3],
     [tab4, 4],
-    [tab5, 5],
-    [tab6, 6],
   ]);
   Assert.equal(tab1.group, group1, "tab1 should be in group1");
+  Assert.equal(
+    tab1.group.firstChild.className,
+    "tab-group-label-container",
+    "Group label appears before the first group tab"
+  );
 
   gBrowser.moveTabForward();
   info("selected tab should move to the end of group1");
@@ -192,8 +189,6 @@ add_task(async function test_moveTabForwardTabGroups() {
     [tab2, 1],
     [tab3, 2],
     [tab4, 4],
-    [tab5, 5],
-    [tab6, 6],
   ]);
   Assert.equal(tab1.group, group1, "tab1 should still be in group1");
 
@@ -204,8 +199,6 @@ add_task(async function test_moveTabForwardTabGroups() {
     [tab2, 1],
     [tab3, 2],
     [tab4, 4],
-    [tab5, 5],
-    [tab6, 6],
   ]);
   Assert.ok(!tab1.group, "tab1 should no longer be in a group");
 
@@ -216,8 +209,6 @@ add_task(async function test_moveTabForwardTabGroups() {
     [tab2, 1],
     [tab3, 2],
     [tab4, 4],
-    [tab5, 5],
-    [tab6, 6],
   ]);
   Assert.equal(tab1.group, group2, "tab1 should now be in group2");
 
@@ -228,8 +219,6 @@ add_task(async function test_moveTabForwardTabGroups() {
     [tab2, 1],
     [tab3, 2],
     [tab4, 3],
-    [tab5, 5],
-    [tab6, 6],
   ]);
   Assert.equal(tab1.group, group2, "tab1 should still be in group2");
 
@@ -240,8 +229,6 @@ add_task(async function test_moveTabForwardTabGroups() {
     [tab2, 1],
     [tab3, 2],
     [tab4, 3],
-    [tab5, 5],
-    [tab6, 6],
   ]);
   Assert.ok(!tab1.group, "tab1 should no longer be in a group");
 
@@ -249,8 +236,6 @@ add_task(async function test_moveTabForwardTabGroups() {
   await removeTabGroup(group2);
   BrowserTestUtils.removeTab(tab1);
   BrowserTestUtils.removeTab(tab2);
-  BrowserTestUtils.removeTab(tab5);
-  BrowserTestUtils.removeTab(tab6);
 });
 
 /* TODO Bug 1927844 for moving the active tab around collapsed tab groups */
@@ -400,117 +385,93 @@ add_task(async function test_moveTabBackwardPinnedTabs() {
 });
 
 add_task(async function test_moveTabBackwardTabGroups() {
-  let tab1 = BrowserTestUtils.addTab(gBrowser, "about:blank");
-  let tab2 = BrowserTestUtils.addTab(gBrowser, "about:blank");
-  let tab3 = BrowserTestUtils.addTab(gBrowser, "about:blank");
-  let tab4 = BrowserTestUtils.addTab(gBrowser, "about:blank");
-  let tab5 = BrowserTestUtils.addTab(gBrowser, "about:blank");
-  let tab6 = BrowserTestUtils.addTab(gBrowser, "about:blank");
-  let group1 = gBrowser.addTabGroup([tab3], { insertBefore: tab3 });
-  let group2 = gBrowser.addTabGroup([tab4], { insertBefore: tab4 });
-  gBrowser.selectedTab = tab6;
+  let win = await BrowserTestUtils.openNewBrowserWindow();
+  let tab1 = win.gBrowser.tabs[0];
+  let tab2 = BrowserTestUtils.addTab(win.gBrowser, "about:blank");
+  let tab3 = BrowserTestUtils.addTab(win.gBrowser, "about:blank");
+  let tab4 = BrowserTestUtils.addTab(win.gBrowser, "about:blank");
+  let group1 = win.gBrowser.addTabGroup([tab1], { insertBefore: tab1 });
+  let group2 = win.gBrowser.addTabGroup([tab3], { insertBefore: tab3 });
+  win.gBrowser.selectedTab = tab4;
 
   info("validate the starting order of the tabs");
   assertTabIndexesMatch([
-    [tab1, 1],
-    [tab2, 2],
-    [tab3, 3],
-    [tab4, 4],
-    [tab5, 5],
-    [tab6, 6],
+    [tab1, 0],
+    [tab2, 1],
+    [tab3, 2],
+    [tab4, 3],
   ]);
-  Assert.ok(!tab6.group, "tab6 should not be in a tab group");
+  Assert.ok(!tab4.group, "tab4 should not be in a tab group");
 
-  gBrowser.moveTabBackward();
-  info("last two tabs should switch places");
-  assertTabIndexesMatch([
-    [tab1, 1],
-    [tab2, 2],
-    [tab3, 3],
-    [tab4, 4],
-    [tab5, 6],
-    [tab6, 5],
-  ]);
-  Assert.ok(!tab6.group, "tab6 should not be in a tab group");
-
-  gBrowser.moveTabBackward();
+  win.gBrowser.moveTabBackward();
   info("selected tab should move into the end of group2");
   assertTabIndexesMatch([
-    [tab1, 1],
-    [tab2, 2],
-    [tab3, 3],
-    [tab4, 4],
-    [tab5, 6],
-    [tab6, 5],
+    [tab1, 0],
+    [tab2, 1],
+    [tab3, 2],
+    [tab4, 3],
   ]);
-  Assert.equal(tab6.group, group2, "tab6 should be in group2");
+  Assert.equal(tab4.group, group2, "tab4 should be in group2");
 
-  gBrowser.moveTabBackward();
+  win.gBrowser.moveTabBackward();
   info("selected tab should move to the start of group2");
   assertTabIndexesMatch([
-    [tab1, 1],
-    [tab2, 2],
+    [tab1, 0],
+    [tab2, 1],
     [tab3, 3],
-    [tab4, 5],
-    [tab5, 6],
-    [tab6, 4],
+    [tab4, 2],
   ]);
-  Assert.equal(tab6.group, group2, "tab6 should still be in group2");
+  Assert.equal(tab4.group, group2, "tab4 should still be in group2");
 
-  gBrowser.moveTabBackward();
+  win.gBrowser.moveTabBackward();
   info("selected tab should become a standalone tab between group1 and group2");
   assertTabIndexesMatch([
-    [tab1, 1],
-    [tab2, 2],
+    [tab1, 0],
+    [tab2, 1],
     [tab3, 3],
-    [tab4, 5],
-    [tab5, 6],
-    [tab6, 4],
+    [tab4, 2],
   ]);
-  Assert.ok(!tab6.group, "tab6 should no longer be in a group");
+  Assert.ok(!tab4.group, "tab4 should no longer be in a group");
+
+  win.gBrowser.moveTabBackward();
+  info("tab should be in between groups. next move should group it.");
+  win.gBrowser.moveTabBackward();
 
-  gBrowser.moveTabBackward();
   info("selected tab should move into the end of group1");
   assertTabIndexesMatch([
-    [tab1, 1],
+    [tab1, 0],
     [tab2, 2],
     [tab3, 3],
-    [tab4, 5],
-    [tab5, 6],
-    [tab6, 4],
+    [tab4, 1],
   ]);
-  Assert.equal(tab6.group, group1, "tab6 should now be in group1");
 
-  gBrowser.moveTabBackward();
+  Assert.equal(tab4.group, group1, "tab4 should now be in group1");
+  win.gBrowser.moveTabBackward();
+
   info("selected tab should move to the start of group1");
   assertTabIndexesMatch([
     [tab1, 1],
     [tab2, 2],
-    [tab3, 4],
-    [tab4, 5],
-    [tab5, 6],
-    [tab6, 3],
+    [tab3, 3],
+    [tab4, 0],
   ]);
-  Assert.equal(tab6.group, group1, "tab6 should still be in group2");
+  Assert.equal(tab4.group, group1, "tab4 should still be in group1");
 
-  gBrowser.moveTabBackward();
+  win.gBrowser.moveTabBackward();
   info("selected tab should become a standalone tab before group1");
   assertTabIndexesMatch([
     [tab1, 1],
     [tab2, 2],
-    [tab3, 4],
-    [tab4, 5],
-    [tab5, 6],
-    [tab6, 3],
+    [tab3, 3],
+    [tab4, 0],
   ]);
-  Assert.ok(!tab6.group, "tab6 should no longer be in a group");
+  Assert.ok(!tab4.group, "tab4 should no longer be in a group");
 
   await removeTabGroup(group1);
   await removeTabGroup(group2);
-  BrowserTestUtils.removeTab(tab1);
   BrowserTestUtils.removeTab(tab2);
-  BrowserTestUtils.removeTab(tab5);
-  BrowserTestUtils.removeTab(tab6);
+  BrowserTestUtils.removeTab(tab4);
+  await BrowserTestUtils.closeWindow(win);
 });
 
 /* TODO Bug 1927844 for moving the active tab around collapsed tab groups */