--- a/browser/base/content/test/webrtc/browser_devices_get_user_media_tear_off_tab.js
+++ b/browser/base/content/test/webrtc/browser_devices_get_user_media_tear_off_tab.js
@@ -44,20 +44,22 @@ var gTests = [
     ok(gIdentityHandler._identityPopup.hidden,
        "control center should be hidden in the first window");
     win.gIdentityHandler._identityPopup.hidden = true;
 
     // Closing the new window should remove all sharing indicators.
     // We need to load the content script in the first window so that we can
     // catch the notifications fired globally when closing the second window.
     gBrowser.selectedBrowser.messageManager.loadFrameScript(CONTENT_SCRIPT_HELPER, true);
-    yield BrowserTestUtils.closeWindow(win);
 
-    yield expectObserverCalled("recording-window-ended");
-    yield expectObserverCalled("recording-device-events");
+    let promises = [promiseObserverCalled("recording-device-events"),
+                    promiseObserverCalled("recording-window-ended")];
+    yield BrowserTestUtils.closeWindow(win);
+    yield Promise.all(promises);
+
     yield expectNoObserverCalled();
     yield checkNotSharing();
   }
 }
 
 ];
 
 function test() {