diff --git a/browser/components/sessionstore/test/browser/browser_490040.js b/browser/components/sessionstore/test/browser/browser_490040.js
index 3645b76b9dfa..9728a7ffc573 100644
--- a/browser/components/sessionstore/test/browser/browser_490040.js
+++ b/browser/components/sessionstore/test/browser/browser_490040.js
@@ -35,8 +35,21 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
+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() {
   /** Test for Bug 490040 **/
+  is(browserWindowsCount(), 1, "Only one browser window should be open initially");
 
   let ss = Cc["@mozilla.org/browser/sessionstore;1"].
            getService(Ci.nsISessionStore);
@@ -154,6 +167,7 @@ function test() {
     else {
       if (gPrefService.prefHasUserValue("browser.sessionstore.max_windows_undo"))
         gPrefService.clearUserPref("browser.sessionstore.max_windows_undo");
+      is(browserWindowsCount(), 1, "Only one browser window should be open eventually");
       finish();
     }
   }
diff --git a/browser/components/sessionstore/test/browser/browser_491168.js b/browser/components/sessionstore/test/browser/browser_491168.js
index b6bbd6a3adc9..4cd224cb72c4 100644
--- a/browser/components/sessionstore/test/browser/browser_491168.js
+++ b/browser/components/sessionstore/test/browser/browser_491168.js
@@ -34,8 +34,21 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
+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() {
   /** Test for Bug 491168 **/
+  is(browserWindowsCount(), 1, "Only one browser window should be open initially");
 
   // test setup
   let ss = Cc["@mozilla.org/browser/sessionstore;1"].getService(Ci.nsISessionStore);
@@ -72,6 +85,7 @@ function test() {
         is(window.content.document.referrer, REFERRER2, "document.referrer is still correct after closing and reopening the tab.");
         gBrowser.removeTab(newTab);
 
+        is(browserWindowsCount(), 1, "Only one browser window should be open eventually");
         finish();
       }, true);
     }, true);
diff --git a/browser/components/sessionstore/test/browser/browser_491577.js b/browser/components/sessionstore/test/browser/browser_491577.js
index c990e61f14b2..b068c7f17a6c 100644
--- a/browser/components/sessionstore/test/browser/browser_491577.js
+++ b/browser/components/sessionstore/test/browser/browser_491577.js
@@ -35,8 +35,21 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
+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() {
   /** Test for Bug 491577 **/
+  is(browserWindowsCount(), 1, "Only one browser window should be open initially");
   
   // test setup
   let ss = Cc["@mozilla.org/browser/sessionstore;1"].getService(Ci.nsISessionStore);
@@ -149,6 +162,7 @@ function test() {
 
     // clean up
     newWin.close();
+    is(browserWindowsCount(), 1, "Only one browser window should be open eventually");
     if (gPrefService.prefHasUserValue("browser.sessionstore.max_windows_undo"))
       gPrefService.clearUserPref("browser.sessionstore.max_windows_undo");
     finish();
diff --git a/browser/components/sessionstore/test/browser/browser_493467.js b/browser/components/sessionstore/test/browser/browser_493467.js
index 9a0d55e2cbb3..5359f243cecb 100644
--- a/browser/components/sessionstore/test/browser/browser_493467.js
+++ b/browser/components/sessionstore/test/browser/browser_493467.js
@@ -34,8 +34,21 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
+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() {
   /** Test for Bug 493467 **/
+  is(browserWindowsCount(), 1, "Only one browser window should be open initially");
   
   let ss = Cc["@mozilla.org/browser/sessionstore;1"].getService(Ci.nsISessionStore);
   
@@ -66,4 +79,5 @@ function test() {
   // leading "allow") to nsSessionStore.js's CAPABILITIES array. Thanks.
   
   gBrowser.removeTab(tab);
+  is(browserWindowsCount(), 1, "Only one browser window should be open eventually");
 }
diff --git a/browser/components/sessionstore/test/browser/browser_495495.js b/browser/components/sessionstore/test/browser/browser_495495.js
index 42d569be35e6..7c2faaadd1d2 100644
--- a/browser/components/sessionstore/test/browser/browser_495495.js
+++ b/browser/components/sessionstore/test/browser/browser_495495.js
@@ -34,8 +34,21 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
+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() {
   /** Test for Bug 495495 **/
+  is(browserWindowsCount(), 1, "Only one browser window should be open initially");
   
   let ss = Cc["@mozilla.org/browser/sessionstore;1"].getService(Ci.nsISessionStore);
   waitForExplicitFinish();
@@ -79,7 +92,10 @@ function test() {
 
           testState(state1, {readOnly: false, enablehistory: "true"}, function() {
             testState(state2, {readOnly: true, enablehistory: "false"}, function() {
-              executeSoon(finish);
+              executeSoon(function () {
+                is(browserWindowsCount(), 1, "Only one browser window should be open eventually");
+                finish();
+              });
             });
           });
         });