--- a/devtools/client/responsive.html/browser/swap.js
+++ b/devtools/client/responsive.html/browser/swap.js
@@ -207,16 +207,25 @@ function addXULBrowserDecorations(browse
     Object.defineProperty(browser, "messageManager", {
       get() {
         return this.frameLoader.messageManager;
       },
       configurable: true,
       enumerable: true,
     });
   }
+  if (browser.outerWindowID == undefined) {
+    Object.defineProperty(browser, "outerWindowID", {
+      get() {
+        return browser._outerWindowID;
+      },
+      configurable: true,
+      enumerable: true,
+    });
+  }
 
   // It's not necessary for these to actually do anything.  These properties are
   // swapped between browsers in browser.xml's `swapDocShells`, and then their
   // `swapBrowser` methods are called, so we define them here for that to work
   // without errors.  During the swap process above, these will move from the
   // the new inner browser to the original tab's browser (step 4) and then to
   // the temporary container tab's browser (step 7), which is then closed.
   if (browser._remoteWebNavigationImpl == undefined) {