--- a/testing/mochitest/runrobocop.py
+++ b/testing/mochitest/runrobocop.py
@@ -221,24 +221,29 @@ class RobocopTestRunner(MochitestDesktop
         """
         self.options.extraPrefs.append('browser.search.suggest.enabled=true')
         self.options.extraPrefs.append('browser.search.suggest.prompted=true')
         self.options.extraPrefs.append('layout.css.devPixelsPerPx=1.0')
         self.options.extraPrefs.append('browser.chrome.dynamictoolbar=false')
         self.options.extraPrefs.append('browser.snippets.enabled=false')
         self.options.extraPrefs.append('browser.casting.enabled=true')
         self.options.extraPrefs.append('extensions.autoupdate.enabled=false')
+
+        self.options.extensionsToExclude.extend([
+            'mochikit@mozilla.org',
+            'worker-test@mozilla.org.xpi',
+            'workerbootstrap-test@mozilla.org.xpi',
+            'indexedDB-signed.xpi',
+        ])
+
         manifest = MochitestDesktop.buildProfile(self, self.options)
         self.localProfile = self.options.profilePath
         self.log.debug("Profile created at %s" % self.localProfile)
         # some files are not needed for robocop; save time by not pushing
         shutil.rmtree(os.path.join(self.localProfile, 'webapps'))
-        desktop_extensions = ['mochikit@mozilla.org', 'worker-test@mozilla.org', 'workerbootstrap-test@mozilla.org', 'indexedDB-test@mozilla.org']
-        for ext in desktop_extensions:
-            shutil.rmtree(os.path.join(self.localProfile, 'extensions', 'staged', ext))
         os.remove(os.path.join(self.localProfile, 'userChrome.css'))
         try:
             self.dm.pushDir(self.localProfile, self.remoteProfileCopy)
         except mozdevice.DMError:
             self.log.error(
                 "Automation Error: Unable to copy profile to device.")
             raise