Bug 1271330 - Avoid homepage overrides in the default profile; r=davehunt,whimboo

MozReview-Commit-ID: 6vQ5C2x7pEB

--HG--
extra : rebase_source : 13a9cbc8cef2a1ca85a8f709452985dbddf92f7c

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,