--- a/testing/firefox-ui/harness/firefox_ui_harness/arguments/update.py
+++ b/testing/firefox-ui/harness/firefox_ui_harness/arguments/update.py
@@ -13,44 +13,38 @@ class UpdateBaseArguments(object):
             'default': [],
             'action': 'append',
             'metavar': 'MAR_CHANNEL',
             'help': 'Additional MAR channel to be allowed for updates, '
                     'e.g. "firefox-mozilla-beta" for updating a release '
                     'build to the latest beta build.'
         }],
         [['--update-channel'], {
-            'dest': 'update_channel',
             'metavar': 'CHANNEL',
             'help': 'Channel to use for the update check.'
         }],
         [['--update-direct-only'], {
-            'dest': 'update_direct_only',
             'default': False,
             'action': 'store_true',
             'help': 'Only perform a direct update'
         }],
         [['--update-fallback-only'], {
-            'dest': 'update_fallback_only',
             'default': False,
             'action': 'store_true',
             'help': 'Only perform a fallback update'
         }],
-        [['--update-override-url'], {
-            'dest': 'update_override_url',
+        [['--update-url'], {
             'metavar': 'URL',
             'help': 'Force specified URL to use for update checks.'
         }],
         [['--update-target-version'], {
-            'dest': 'update_target_version',
             'metavar': 'VERSION',
             'help': 'Version of the updated build.'
         }],
         [['--update-target-buildid'], {
-            'dest': 'update_target_buildid',
             'metavar': 'BUILD_ID',
             'help': 'Build ID of the updated build.'
         }],
     ]
 
     def verify_usage_handler(self, args):
         if args.update_direct_only and args.update_fallback_only:
             raise ValueError('Arguments --update-direct-only and --update-fallback-only '

--- a/testing/firefox-ui/harness/firefox_ui_harness/runners/update.py
+++ b/testing/firefox-ui/harness/firefox_ui_harness/runners/update.py
@@ -21,21 +21,16 @@ class UpdateTestRunner(FirefoxUITestRunn
 
     def __init__(self, **kwargs):
         super(UpdateTestRunner, self).__init__(**kwargs)
 
         self.original_bin = self.bin
 
         self.prefs.update(DEFAULT_PREFS)
 
-        # In case of overriding the update URL, set the appropriate preference
-        override_url = kwargs.pop('update_override_url', None)
-        if override_url:
-            self.prefs.update({'app.update.url.override': override_url})
-
         self.run_direct_update = not kwargs.pop('update_fallback_only', False)
         self.run_fallback_update = not kwargs.pop('update_direct_only', False)
 
         self.test_handlers = [UpdateTestCase]
 
     def run_tests(self, tests):
         # Used to store the last occurred exception because we execute
         # run_tests() multiple times

--- a/testing/firefox-ui/harness/firefox_ui_harness/testcases.py
+++ b/testing/firefox-ui/harness/firefox_ui_harness/testcases.py
@@ -31,16 +31,18 @@ class UpdateTestCase(PuppeteerMixin, Mar
     # raised. See:
     # http://mxr.mozilla.org/mozilla-central/source/toolkit/mozapps/update/nsUpdateService.js?rev=a9240b1eb2fb#4813
     # http://mxr.mozilla.org/mozilla-central/source/toolkit/mozapps/update/nsUpdateService.js?rev=a9240b1eb2fb#4756
     PREF_APP_UPDATE_ALTWINDOWTYPE = 'app.update.altwindowtype'
 
     def __init__(self, *args, **kwargs):
         super(UpdateTestCase, self).__init__(*args, **kwargs)
 
+        self.update_url = kwargs.pop('update_url')
+
         self.target_buildid = kwargs.pop('update_target_buildid')
         self.target_version = kwargs.pop('update_target_version')
 
         self.update_channel = kwargs.pop('update_channel')
         self.default_update_channel = None
 
         self.update_mar_channels = set(kwargs.pop('update_mar_channels'))
         self.default_mar_channels = None
@@ -54,16 +56,18 @@ class UpdateTestCase(PuppeteerMixin, Mar
         self.download_duration = None
 
         # Bug 604364 - Preparation to test multiple update steps
         self.current_update_index = 0
 
         # Ensure that there exists no already partially downloaded update
         self.remove_downloaded_update()
 
+        self.set_preferences_defaults()
+
         # If requested modify the default update channel. It will be active
         # after the next restart of the application
         # Bug 1142805 - Modify file via Python directly
         if self.update_channel:
             # Backup the original content and the path of the channel-prefs.js file
             self.default_update_channel = {
                 'content': self.software_update.update_channel.file_contents,
                 'path': self.software_update.update_channel.file_path,
@@ -365,16 +369,23 @@ class UpdateTestCase(PuppeteerMixin, Mar
         """Remove an already downloaded update from the update staging directory.
 
         Hereby not only remove the update subdir but everything below 'updates'.
         """
         path = os.path.dirname(self.software_update.staging_directory)
         self.logger.info('Clean-up update staging directory: {}'.format(path))
         mozfile.remove(path)
 
+    def restart(self, *args, **kwargs):
+        super(UpdateTestCase, self).restart(*args, **kwargs)
+
+        # After a restart default preference values as set in the former session are lost.
+        # Make sure that any of those are getting restored.
+        self.set_preferences_defaults()
+
     def restore_config_files(self):
         # Reset channel-prefs.js file if modified
         try:
             if self.default_update_channel:
                 path = self.default_update_channel['path']
                 self.logger.info('Restoring channel defaults for: {}'.format(path))
                 with open(path, 'w') as f:
                     f.write(self.default_update_channel['content'])
@@ -388,16 +399,22 @@ class UpdateTestCase(PuppeteerMixin, Mar
                 path = self.default_mar_channels['path']
                 self.logger.info('Restoring mar channel defaults for: {}'.format(path))
                 with open(path, 'w') as f:
                     f.write(self.default_mar_channels['content'])
         except IOError:
             self.logger.error('Failed to reset the default mar channels.',
                               exc_info=True)
 
+    def set_preferences_defaults(self):
+        """Set the default value for specific preferences to force its usage."""
+        if self.update_url:
+            self.puppeteer.prefs.set_pref("app.update.url", self.update_url,
+                                          default_branch=True)
+
     def wait_for_download_finished(self, window, timeout=TIMEOUT_UPDATE_DOWNLOAD):
         """ Waits until download is completed.
 
         :param window: Instance of :class:`AboutWindow` or :class:`UpdateWizardDialog`.
         :param timeout: How long to wait for the download to finish. Optional,
          default to 360 seconds.
         """
         # The old update wizard dialog has to be handled differently. It's necessary