diff --git a/browser/base/content/test/browser_bug416661.js b/browser/base/content/test/browser_bug416661.js
index e4d0d28043b9..f459284eeeba 100644
--- a/browser/base/content/test/browser_bug416661.js
+++ b/browser/base/content/test/browser_bug416661.js
@@ -43,7 +43,8 @@ function test() {
 }
 
 function afterZoomAndLoad(cb) {
-  let didLoad = didZoom = false;
+  let didLoad = false;
+  let didZoom = false;
   tabElm.linkedBrowser.addEventListener("load", function() {
     tabElm.linkedBrowser.removeEventListener("load", arguments.callee, true);
     didLoad = true;
diff --git a/browser/base/content/test/browser_bug555224.js b/browser/base/content/test/browser_bug555224.js
index 3e1a483e2e7e..b0cff4eec730 100644
--- a/browser/base/content/test/browser_bug555224.js
+++ b/browser/base/content/test/browser_bug555224.js
@@ -37,7 +37,8 @@ const TEST_PAGE = "/browser/browser/base/content/test/dummy_page.html";
 var gTestTab, gBgTab, gTestZoom;
 
 function afterZoomAndLoad(aCallback, aTab) {
-  let didLoad = didZoom = false;
+  let didLoad = false;
+  let didZoom = false;
   aTab.linkedBrowser.addEventListener("load", function() {
     aTab.linkedBrowser.removeEventListener("load", arguments.callee, true);
     didLoad = true;
diff --git a/browser/base/content/test/browser_bug592338.js b/browser/base/content/test/browser_bug592338.js
index 61414811bff4..a9ec62566739 100644
--- a/browser/base/content/test/browser_bug592338.js
+++ b/browser/base/content/test/browser_bug592338.js
@@ -4,7 +4,9 @@
 
 const TESTROOT = "http://example.com/browser/toolkit/mozapps/extensions/test/xpinstall/";
 
-Components.utils.import("resource://gre/modules/LightweightThemeManager.jsm");
+var tempScope = {};
+Components.utils.import("resource://gre/modules/LightweightThemeManager.jsm", tempScope);
+var LightweightThemeManager = tempScope.LightweightThemeManager;
 
 function wait_for_notification(aCallback) {
   PopupNotifications.panel.addEventListener("popupshown", function() {
diff --git a/browser/base/content/test/browser_bug623155.js b/browser/base/content/test/browser_bug623155.js
index 3a36d2a1148f..7a09e3e4ecf2 100644
--- a/browser/base/content/test/browser_bug623155.js
+++ b/browser/base/content/test/browser_bug623155.js
@@ -43,6 +43,8 @@ https://example.com/browser/browser/base/content/test/redirect_bug623155.sjs#FG
 
  */
 
+var gNewTab;
+
 function test() {
   waitForExplicitFinish();
 
diff --git a/browser/base/content/test/browser_gestureSupport.js b/browser/base/content/test/browser_gestureSupport.js
index 1a7a5f609fbb..054251bb51ef 100644
--- a/browser/base/content/test/browser_gestureSupport.js
+++ b/browser/base/content/test/browser_gestureSupport.js
@@ -383,7 +383,7 @@ function test_latchedGesture(gesture, inc, dec, eventPrefix)
 
   // Restore the gesture to its original configuration.
   gPrefService.setBoolPref(branch + "latched", oldLatchedValue);
-  for (dir in cmd)
+  for (let dir in cmd)
     test_removeCommand(cmd[dir]);
 }
 
diff --git a/browser/base/content/test/browser_identity_UI.js b/browser/base/content/test/browser_identity_UI.js
index ba220ea6c93c..b0e32d32297d 100644
--- a/browser/base/content/test/browser_identity_UI.js
+++ b/browser/base/content/test/browser_identity_UI.js
@@ -68,7 +68,7 @@ var tests = [
   },
 ]
 
-let gCurrentTest, gCurrentTestIndex = -1;
+let gCurrentTest, gCurrentTestIndex = -1, gTestDesc;
 // Go through the tests in both directions, to add additional coverage for
 // transitions between different states.
 let gForward = true;
diff --git a/testing/mochitest/tests/SimpleTest/SimpleTest.js b/testing/mochitest/tests/SimpleTest/SimpleTest.js
index 6a933fa07738..493048ab192c 100644
--- a/testing/mochitest/tests/SimpleTest/SimpleTest.js
+++ b/testing/mochitest/tests/SimpleTest/SimpleTest.js
@@ -611,7 +611,7 @@ SimpleTest.waitForClipboard = function(aExpectedStringOrValidatorFn, aSetupFn,
             return;
         }
 
-        data = SpecialPowers.getClipboardData(flavor);
+        var data = SpecialPowers.getClipboardData(flavor);
 
         if (validatorFn(data)) {
             // Don't show the success message when waiting for preExpectedVal
diff --git a/testing/mochitest/tests/SimpleTest/specialpowersAPI.js b/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
index e9196828d5a6..3f17f8980995 100644
--- a/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
+++ b/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
@@ -934,7 +934,7 @@ SpecialPowersAPI.prototype = {
 
   // :jdm gets credit for this.  ex: getPrivilegedProps(window, 'location.href');
   getPrivilegedProps: function(obj, props) {
-    parts = props.split('.');
+    var parts = props.split('.');
 
     for (var i = 0; i < parts.length; i++) {
       var p = parts[i];