--- a/testing/marionette/harness/marionette_harness/tests/unit/test_modal_dialogs.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_modal_dialogs.py
@@ -8,32 +8,34 @@ from marionette_driver.marionette import
 from marionette_driver.wait import Wait
 
 from marionette_harness import MarionetteTestCase, skip_if_e10s
 
 
 class TestTabModals(MarionetteTestCase):
 
     def setUp(self):
-        MarionetteTestCase.setUp(self)
-        self.marionette.enforce_gecko_prefs({"prompts.tab_modal.enabled": True})
+        super(TestTabModals, self).setUp()
+        self.marionette.set_pref("prompts.tab_modal.enabled", True)
         self.marionette.navigate(self.marionette.absolute_url('modal_dialogs.html'))
 
+    def tearDown(self):
+        # Ensure an alert is absent before proceeding past this test.
+        Wait(self.marionette).until(lambda _: not self.alert_present())
+        self.marionette.execute_script("window.onbeforeunload = null;")
+        self.marionette.clear_pref("prompts.tab_modal.enabled")
+        super(TestTabModals, self).tearDown()
+
     def alert_present(self):
         try:
             Alert(self.marionette).text
             return True
         except NoAlertPresentException:
             return False
 
-    def tearDown(self):
-        # Ensure an alert is absent before proceeding past this test.
-        Wait(self.marionette).until(lambda _: not self.alert_present())
-        self.marionette.execute_script("window.onbeforeunload = null;")
-
     def wait_for_alert(self):
         Wait(self.marionette).until(lambda _: self.alert_present())
 
     def test_no_alert_raises(self):
         self.assertRaises(NoAlertPresentException, Alert(self.marionette).accept)
         self.assertRaises(NoAlertPresentException, Alert(self.marionette).dismiss)
 
     def test_alert_accept(self):
@@ -182,16 +184,15 @@ class TestTabModals(MarionetteTestCase):
         click_handler.click()
         text = self.marionette.find_element(By.ID, 'click-result').text
         self.assertEqual(text, 'result')
 
 
 class TestGlobalModals(TestTabModals):
 
     def setUp(self):
-        MarionetteTestCase.setUp(self)
-        self.marionette.enforce_gecko_prefs({"prompts.tab_modal.enabled": False})
-        self.marionette.navigate(self.marionette.absolute_url('modal_dialogs.html'))
+        super(TestGlobalModals, self).setUp()
+        self.marionette.set_pref("prompts.tab_modal.enabled", False)
 
     def test_unrelated_command_when_alert_present(self):
         # The assumptions in this test do not hold on certain platforms, and not when
         # e10s is enabled.
         pass

--- a/testing/marionette/harness/marionette_harness/tests/unit/unit-tests.ini
+++ b/testing/marionette/harness/marionette_harness/tests/unit/unit-tests.ini
@@ -98,17 +98,16 @@ skip-if = true # Bug 925688
 skip-if = manage_instance == false || appname == 'fennec' # Bug 1298921 and bug 1322993
 [test_quit_restart.py]
 skip-if = manage_instance == false || appname == 'fennec' # Bug 1298921 and bug 1322993
 [test_set_window_size.py]
 skip-if = os == "linux" || appname == 'fennec' # Bug 1085717
 [test_with_using_context.py]
 
 [test_modal_dialogs.py]
-skip-if = manage_instance == false || appname == 'fennec' # Bug 1328696
 [test_key_actions.py]
 [test_mouse_action.py]
 skip-if = appname == 'fennec'
 [test_teardown_context_preserved.py]
 [test_file_upload.py]
 skip-if = appname == 'fennec' || os == "win" # http://bugs.python.org/issue14574
 
 [test_execute_sandboxes.py]