--- a/testing/firefox-ui/harness/firefox_ui_harness/runners/update.py
+++ b/testing/firefox-ui/harness/firefox_ui_harness/runners/update.py
@@ -7,16 +7,18 @@ import sys
 import mozfile
 import mozinstall
 
 from firefox_ui_harness.runners import FirefoxUITestRunner
 from firefox_ui_harness.testcases import UpdateTestCase
 
 
 DEFAULT_PREFS = {
+    # Bug 1355026: Re-enable when support for the new simplified UI update is available
+    'app.update.doorhanger': False,
     'app.update.log': True,
     'startup.homepage_override_url': 'about:blank',
 }
 
 
 class UpdateTestRunner(FirefoxUITestRunner):
 
     def __init__(self, **kwargs):