diff --git a/browser/base/content/test/tabs/browser_multiselect_tabs_move_to_new_window_contextmenu.js b/browser/base/content/test/tabs/browser_multiselect_tabs_move_to_new_window_contextmenu.js
index b47a4b3a7d50..347d2f6c0f37 100644
--- a/browser/base/content/test/tabs/browser_multiselect_tabs_move_to_new_window_contextmenu.js
+++ b/browser/base/content/test/tabs/browser_multiselect_tabs_move_to_new_window_contextmenu.js
@@ -47,58 +47,67 @@ add_task(async function test() {
 
 add_task(async function testLazyTabs() {
   let params = {createLazyBrowser: true};
-  let tabs = [];
+  let oldTabs = [];
   let numTabs = 4;
   for (let i = 0; i < numTabs; ++i) {
-    tabs.push(BrowserTestUtils.addTab(gBrowser, `http://example.com/?${i}`, params));
+    oldTabs.push(BrowserTestUtils.addTab(gBrowser, `http://example.com/?${i}`, params));
   }
 
-  await BrowserTestUtils.switchTab(gBrowser, tabs[0]);
+  await BrowserTestUtils.switchTab(gBrowser, oldTabs[0]);
   for (let i = 1; i < numTabs; ++i) {
-    await triggerClickOn(tabs[i], { ctrlKey: true });
+    await triggerClickOn(oldTabs[i], { ctrlKey: true });
   }
 
-  isnot(tabs[0].linkedPanel, "", `Tab 0 shouldn't be lazy`);
+  isnot(oldTabs[0].linkedPanel, "", `Old tab 0 shouldn't be lazy`);
   for (let i = 1; i < numTabs; ++i) {
-    is(tabs[i].linkedPanel, "", `Tab ${i} should be lazy`);
+    is(oldTabs[i].linkedPanel, "", `Old tab ${i} should be lazy`);
   }
 
   is(gBrowser.multiSelectedTabsCount, numTabs, `${numTabs} multiselected tabs`);
   for (let i = 0; i < numTabs; ++i) {
-    ok(tabs[i].multiselected, `Tab ${i} should be multiselected`);
+    ok(oldTabs[i].multiselected, `Old tab ${i} should be multiselected`);
   }
 
   let tabsMoved = new Promise(resolve => {
     // Tab tabs in the new window will be about:blank before swapping the docshells.
     // The "EndSwapDocShells" event is not dispatched for lazy tabs, so listen for
     // "TabClose" instead and await a tick.
-    let i = 0;
-    window.addEventListener("TabClose", async function listener() {
+    let numTabsMoved = 0;
+    window.addEventListener("TabClose", async function listener(event) {
+      let tab = event.target;
+      let i = oldTabs.indexOf(tab);
+      if (i == 0) {
+        isnot(tab.linkedPanel, "", `Old tab ${i} should continue not being lazy`);
+      } else if (i > 0) {
+        is(tab.linkedPanel, "", `Old tab ${i} should continue being lazy`);
+      } else {
+        return;
+      }
       await Promise.resolve();
-      if (++i == numTabs) {
+      if (++numTabsMoved == numTabs) {
         window.removeEventListener("TabClose", listener);
         resolve();
       }
     });
   });
-  let newWindow = gBrowser.replaceTabsWithWindow(tabs[0]);
+  let newWindow = gBrowser.replaceTabsWithWindow(oldTabs[0]);
   await tabsMoved;
-  tabs = newWindow.gBrowser.tabs;
+  let newTabs = newWindow.gBrowser.tabs;
 
-  isnot(tabs[0].linkedPanel, "", `Tab 0 should continue not being lazy`);
+  isnot(newTabs[0].linkedPanel, "", `New tab 0 should continue not being lazy`);
   // FIXME: bug 1521923 - First inactive tab to be moved into another window loses laziness
-  todo_is(tabs[1].linkedPanel, "", `Tab 1 should continue being lazy`);
+  todo_is(newTabs[1].linkedPanel, "", `New tab 1 should continue being lazy`);
   for (let i = 2; i < numTabs; ++i) {
-    is(tabs[i].linkedPanel, "", `Tab ${i} should continue being lazy`);
+    is(newTabs[i].linkedPanel, "", `New tab ${i} should continue being lazy`);
   }
 
-  is(tabs[0].linkedBrowser.currentURI.spec, `http://example.com/?0`,
-    `Tab 0 should have the right URL`);
-  todo_is(SessionStore.getLazyTabValue(tabs[1], "url"), `http://example.com/?1`,
-    `Tab 1 should have the right lazy URL`);
+  is(newTabs[0].linkedBrowser.currentURI.spec, `http://example.com/?0`,
+    `New tab 0 should have the right URL`);
+  todo_is(SessionStore.getLazyTabValue(newTabs[1], "url"), `http://example.com/?1`,
+    `New tab 1 should have the right lazy URL`);
   for (let i = 2; i < numTabs; ++i) {
-    is(SessionStore.getLazyTabValue(tabs[i], "url"), `http://example.com/?${i}`,
-      `Tab ${i} should have the right lazy URL`);
+    is(SessionStore.getLazyTabValue(newTabs[i], "url"), `http://example.com/?${i}`,
+      `New tab ${i} should have the right lazy URL`);
   }
 
   BrowserTestUtils.closeWindow(newWindow);
diff --git a/browser/components/extensions/parent/ext-browser.js b/browser/components/extensions/parent/ext-browser.js
index 7ba6534db938..c74ec9db370e 100644
--- a/browser/components/extensions/parent/ext-browser.js
+++ b/browser/components/extensions/parent/ext-browser.js
@@ -454,10 +454,11 @@ class TabTracker extends TabTrackerBase {
           // This tab is being created to adopt a tab from a different window.
           // Handle the adoption.
           this.adopt(nativeTab, adoptedTab);
-
-          adoptedTab.linkedBrowser.messageManager.sendAsyncMessage("Extension:SetFrameData", {
-            windowId: windowTracker.getId(nativeTab.ownerGlobal),
-          });
+          if (adoptedTab.linkedPanel) {
+            adoptedTab.linkedBrowser.messageManager.sendAsyncMessage("Extension:SetFrameData", {
+              windowId: windowTracker.getId(nativeTab.ownerGlobal),
+            });
+          }
         } else {
           // Save the size of the current tab, since the newly-created tab will
           // likely be active by the time the promise below resolves and the