diff --git a/testing/marionette/client/marionette_driver/geckoinstance.py b/testing/marionette/client/marionette_driver/geckoinstance.py
index 7e8201ef90f7..f75a43e1a017 100644
--- a/testing/marionette/client/marionette_driver/geckoinstance.py
+++ b/testing/marionette/client/marionette_driver/geckoinstance.py
@@ -17,6 +17,8 @@ class GeckoInstance(object):
     required_prefs = {
         "browser.sessionstore.resume_from_crash": False,
         "browser.shell.checkDefaultBrowser": False,
+        # Needed for branded builds to prevent opening a second tab on startup
+        "browser.startup.homepage_override.mstone": "ignore",
         "browser.startup.page": 0,
         "browser.tabs.remote.autostart.1": False,
         "browser.tabs.remote.autostart.2": False,