diff --git a/browser/components/sessionstore/test/browser/browser_354894.js b/browser/components/sessionstore/test/browser/browser_354894.js
index 0072c67b8093..c68ca8af0576 100644
--- a/browser/components/sessionstore/test/browser/browser_354894.js
+++ b/browser/components/sessionstore/test/browser/browser_354894.js
@@ -104,7 +104,22 @@
  * nsSessionStore restore a window next time it gets a chance and will post
  * notifications. The latter won't.
  */
+
+function browserWindowsCount() {
+  let count = 0;
+  let e = Cc["@mozilla.org/appshell/window-mediator;1"]
+            .getService(Ci.nsIWindowMediator)
+            .getEnumerator("navigator:browser");
+  while (e.hasMoreElements()) {
+    if (!e.getNext().closed)
+      ++count;
+  }
+  return count;
+}
+
 function test() {
+  is(browserWindowsCount(), 1, "Only one browser window should be open initially");
+
   waitForExplicitFinish();
 
   // Some urls that might be opened in tabs and/or popups
@@ -217,9 +232,9 @@ function test() {
       newWin.removeEventListener("load", arguments.callee, false);
       newWin.gBrowser.addEventListener("load", function(aEvent) {
         newWin.gBrowser.removeEventListener("load", arguments.callee, true);
-        for each (let url in TEST_URLS) {
+        TEST_URLS.forEach(function (url) {
           newWin.gBrowser.addTab(url);
-        }
+        });
 
         executeSoon(function() testFn(newWin));
       }, true);
@@ -498,7 +513,11 @@ function test() {
     // Mac tests
     testMacNotifications(
       function() testNotificationCount(
-        function() cleanupTestsuite() + finish()
+        function() {
+          cleanupTestsuite();
+          is(browserWindowsCount(), 1, "Only one browser window should be open eventually");
+          finish();
+        }
       )
     );
   }
@@ -510,7 +529,11 @@ function test() {
           function() testOpenCloseOnlyPopup(
             function() testOpenCloseRestoreFromPopup (
               function() testNotificationCount(
-                function() cleanupTestsuite() + finish()
+                function() {
+                  cleanupTestsuite();
+                  is(browserWindowsCount(), 1, "Only one browser window should be open eventually");
+                  finish();
+                }
               )
             )
           )