new file mode 100644
--- /dev/null
+++ b/toolkit/components/url-classifier/tests/mochitest/classifierCommon.js
@@ -0,0 +1,38 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function doUpdate(update) {
+  const { classes: Cc, interfaces: Ci, results: Cr } = Components;
+
+  let listener = {
+    QueryInterface: function(iid)
+    {
+      if (iid.equals(Ci.nsISupports) ||
+          iid.equals(Ci.nsIUrlClassifierUpdateObserver))
+        return this;
+
+      throw Cr.NS_ERROR_NO_INTERFACE;
+    },
+    updateUrlRequested: function(url) { },
+    streamFinished: function(status) { },
+    updateError: function(errorCode) {
+      sendAsyncMessage("updateError", { errorCode });
+    },
+    updateSuccess: function(requestedTimeout) {
+      sendAsyncMessage("loadTestFrame");
+    }
+  };
+
+  let dbService = Cc["@mozilla.org/url-classifier/dbservice;1"]
+                  .getService(Ci.nsIUrlClassifierDBService);
+
+  dbService.beginUpdate(listener, "test-malware-simple,test-unwanted-simple", "");
+  dbService.beginStream("", "");
+  dbService.updateStream(update);
+  dbService.finishStream();
+  dbService.finishUpdate();
+}
+
+addMessageListener("doUpdate", ({ testUpdate }) => {
+  doUpdate(testUpdate);
+});

--- a/toolkit/components/url-classifier/tests/mochitest/mochitest.ini
+++ b/toolkit/components/url-classifier/tests/mochitest/mochitest.ini
@@ -1,12 +1,13 @@
 [DEFAULT]
-skip-if = buildapp == 'b2g' || e10s
+skip-if = buildapp == 'b2g'
 support-files =
   classifiedAnnotatedPBFrame.html
+  classifierCommon.js
   classifierFrame.html
   cleanWorker.js
   good.js
   evil.css
   evil.js
   evil.js^headers^
   evilWorker.js
   import.css

--- a/toolkit/components/url-classifier/tests/mochitest/test_classifier.html
+++ b/toolkit/components/url-classifier/tests/mochitest/test_classifier.html
@@ -8,77 +8,57 @@
 
 <p id="display"></p>
 <div id="content" style="display: none">
 </div>
 <pre id="test">
 
 <script class="testbody" type="text/javascript">
 
-var Cc = SpecialPowers.Cc;
-var Ci = SpecialPowers.Ci;
 var firstLoad = true;
 
 // Add some URLs to the malware database.
 var testData = "malware.example.com/";
 var testUpdate =
   "n:1000\ni:test-malware-simple\nad:1\n" +
   "a:524:32:" + testData.length + "\n" +
   testData;
 
 testData = "unwanted.example.com/";
 testUpdate +=
   "n:1000\ni:test-unwanted-simple\nad:1\n" +
   "a:524:32:" + testData.length + "\n" +
   testData;
 
-var dbService = Cc["@mozilla.org/url-classifier/dbservice;1"]
-                .getService(Ci.nsIUrlClassifierDBService);
-
 function loadTestFrame() {
   document.getElementById("testFrame").src = "classifierFrame.html";
 }
 
-function doUpdate(update) {
-  var listener = {
-    QueryInterface: SpecialPowers.wrapCallback(function(iid)
-    {
-      if (iid.equals(Ci.nsISupports) ||
-          iid.equals(Ci.nsIUrlClassifierUpdateObserver))
-        return this;
+const CLASSIFIER_COMMON_URL = SimpleTest.getTestFileURL("classifierCommon.js");
+let classifierCommonScript = SpecialPowers.loadChromeScript(CLASSIFIER_COMMON_URL);
+
+// Expected finish() call is in "classifierFrame.html".
+SimpleTest.waitForExplicitFinish();
 
-      throw Cr.NS_ERROR_NO_INTERFACE;
-    }),
-    updateUrlRequested: function(url) { },
-    streamFinished: function(status) { },
-    updateError: function(errorCode) {
-      ok(false, "Couldn't update classifier.");
-      // Abort test.
-      SimpleTest.finish();
-    },
-    updateSuccess: function(requestedTimeout) {
-      SpecialPowers.pushPrefEnv(
-        {"set" : [["browser.safebrowsing.malware.enabled", true]]},
-        loadTestFrame);
-    }
-  };
-
-  dbService.beginUpdate(listener, "test-malware-simple,test-unwanted-simple", "");
-  dbService.beginStream("", "");
-  dbService.updateStream(update);
-  dbService.finishStream();
-  dbService.finishUpdate();
-}
+classifierCommonScript.addMessageListener("loadTestFrame", () => {
+  SpecialPowers.pushPrefEnv(
+    {"set" : [["browser.safebrowsing.malware.enabled", true]]},
+    loadTestFrame);
+});
+classifierCommonScript.addMessageListener("updateError", ({ errorCode }) => {
+  ok(false, "Couldn't update classifier. Error code: " + errorCode);
+  // Abort test.
+  SimpleTest.finish();
+});
 
 SpecialPowers.pushPrefEnv(
   {"set" : [["urlclassifier.malwareTable", "test-malware-simple,test-unwanted-simple"],
             ["urlclassifier.phishTable", "test-phish-simple"]]},
-  function() { doUpdate(testUpdate); });
-
-// Expected finish() call is in "classifierFrame.html".
-SimpleTest.waitForExplicitFinish();
+  function() {
+    classifierCommonScript.sendAsyncMessage("doUpdate", { testUpdate });
+  });
 
 </script>
 
 </pre>
 <iframe id="testFrame" onload=""></iframe>
 </body>
 </html>

--- a/toolkit/components/url-classifier/tests/mochitest/test_classifier_worker.html
+++ b/toolkit/components/url-classifier/tests/mochitest/test_classifier_worker.html
@@ -8,85 +8,65 @@
 
 <p id="display"></p>
 <div id="content" style="display: none">
 </div>
 <pre id="test">
 
 <script class="testbody" type="text/javascript">
 
-var Cc = SpecialPowers.Cc;
-var Ci = SpecialPowers.Ci;
-
 // Add some URLs to the malware database.
 var testData = "example.com/tests/toolkit/components/url-classifier/tests/mochitest/evilWorker.js";
 var testUpdate =
   "n:1000\ni:test-malware-simple\nad:550\n" +
   "a:550:32:" + testData.length + "\n" +
   testData;
 
 testData = "example.com/tests/toolkit/components/url-classifier/tests/mochitest/unwantedWorker.js";
 testUpdate +=
   "n:1000\ni:test-unwanted-simple\nad:550\n" +
   "a:550:32:" + testData.length + "\n" +
   testData;
 
-var dbService = Cc["@mozilla.org/url-classifier/dbservice;1"]
-                .getService(Ci.nsIUrlClassifierDBService);
-
-function doUpdate(update) {
-  var listener = {
-    QueryInterface: SpecialPowers.wrapCallback(function(iid)
-    {
-      if (iid.equals(Ci.nsISupports) ||
-          iid.equals(Ci.nsIUrlClassifierUpdateObserver))
-        return this;
-
-      throw Cr.NS_ERROR_NO_INTERFACE;
-    }),
-    updateUrlRequested: function(url) { },
-    streamFinished: function(status) { },
-    updateError: function(errorCode) {
-      ok(false, "Couldn't update classifier.");
-      // Abort test.
-      SimpleTest.finish();
-    },
-    updateSuccess: function(requestedTimeout) {
-      SpecialPowers.pushPrefEnv(
-        {"set" : [["browser.safebrowsing.malware.enabled", true]]},
-        function loadTestFrame() {
-          document.getElementById("testFrame").src =
-            "http://example.com/tests/toolkit/components/url-classifier/tests/mochitest/workerFrame.html";
-        }
-      );
-    }
-  };
-
-  dbService.beginUpdate(listener, "test-malware-simple,test-unwanted-simple", "");
-  dbService.beginStream("", "");
-  dbService.updateStream(update);
-  dbService.finishStream();
-  dbService.finishUpdate();
+function loadTestFrame() {
+  document.getElementById("testFrame").src =
+    "http://example.com/tests/toolkit/components/url-classifier/tests/mochitest/workerFrame.html";
 }
 
 function onmessage(event)
 {
   var pieces = event.data.split(':');
   if (pieces[0] == "finish") {
     SimpleTest.finish();
     return;
   }
 
   is(pieces[0], "success", pieces[1]);
 }
 
+const CLASSIFIER_COMMON_URL = SimpleTest.getTestFileURL("classifierCommon.js");
+let classifierCommonScript = SpecialPowers.loadChromeScript(CLASSIFIER_COMMON_URL);
+
+classifierCommonScript.addMessageListener("loadTestFrame", () => {
+  SpecialPowers.pushPrefEnv(
+    {"set" : [["browser.safebrowsing.malware.enabled", true]]},
+    loadTestFrame);
+});
+classifierCommonScript.addMessageListener("updateError", ({ errorCode }) => {
+  ok(false, "Couldn't update classifier. Error code: " + errorCode);
+  // Abort test.
+  SimpleTest.finish();
+});
+
 SpecialPowers.pushPrefEnv(
   {"set" : [["urlclassifier.malwareTable", "test-malware-simple,test-unwanted-simple"],
             ["urlclassifier.phishTable", "test-phish-simple"]]},
-  function() { doUpdate(testUpdate); });
+  function() {
+    classifierCommonScript.sendAsyncMessage("doUpdate", { testUpdate });
+  });
 
 window.addEventListener("message", onmessage, false);
 
 SimpleTest.waitForExplicitFinish();
 
 </script>
 
 </pre>