--- a/testing/mozharness/mozharness/mozilla/testing/firefox_ui_tests.py
+++ b/testing/mozharness/mozharness/mozilla/testing/firefox_ui_tests.py
@@ -42,16 +42,20 @@ firefox_ui_tests_config_options = [
         'default': 'https://github.com/mozilla/firefox-ui-tests.git',
         'help': 'which firefox_ui_tests repo to use',
     }],
     [['--symbols-path=SYMBOLS_PATH'], {
         'dest': 'symbols_path',
         'help': 'absolute path to directory containing breakpad '
                 'symbols, or the url of a zip file containing symbols.',
     }],
+    [['--tag=TAG'], {
+        'dest': 'tag',
+        'help': 'Subset of tests to run (local, remote).',
+    }],
 ] + copy.deepcopy(testing_config_options)
 
 # Command line arguments for update tests
 firefox_ui_update_harness_config_options = [
     [['--update-allow-mar-channel'], {
         'dest': 'update_allow_mar_channel',
         'help': 'Additional MAR channel to be allowed for updates, e.g. '
                 '"firefox-mozilla-beta" for updating a release build to '
@@ -255,16 +259,19 @@ class FirefoxUITests(TestingMixin, VCSTo
         env = env or self.query_env()
 
         if self.symbols_url:
             cmd.extend(['--symbols-path', self.symbols_url])
 
         if self.query_minidump_stackwalk():
             env['MINIDUMP_STACKWALK'] = self.minidump_stackwalk_path
 
+        if self.config.get('tag'):
+            cmd.extend(['--tag', self.config['tag']])
+
         parser = StructuredOutputParser(config=self.config,
                                         log_obj=self.log_obj,
                                         strict=False)
 
         # Add the default tests to run
         tests = [os.path.join(dirs['abs_fxui_dir'], 'tests', test) for test in self.default_tests]
         cmd.extend(tests)