Bug 1558763 - [marionette] Disable "browser.tabs.remote.separatePrivilegedContentProcess" by default. r=maja_zf

Due to bug 1557457 it can happen that loading a web page with eg.
a HTTP auth prompt, no modal dialog will be shown by Firefox. As
such disable this preference for now globally, until all the issues
with privileged content processes have been solved.

Differential Revision: https://phabricator.services.mozilla.com/D34710

--HG--
extra : moz-landing-system : lando

testing/marionette/client/marionette_driver/geckoinstance.py

@@ -563,6 +563,9 @@ class DesktopInstance(GeckoInstance):
         # Disable browser animations
         "toolkit.cosmeticAnimations.enabled": False,
 
+        # Bug 1557457: Disable because modal dialogs might not appear in Firefox
+        "browser.tabs.remote.separatePrivilegedContentProcess": False,
+
         # Don't unload tabs when available memory is running low
         "browser.tabs.unloadOnLowMemory": False,
 

testing/marionette/components/marionette.js

@@ -131,6 +131,9 @@ const RECOMMENDED_PREFS = new Map([
   // unloaded
   ["browser.tabs.disableBackgroundZombification", false],
 
+  // Bug 1557457: Disable because modal dialogs might not appear in Firefox
+  ["browser.tabs.remote.separatePrivilegedContentProcess", false],
+
   // Don't unload tabs when available memory is running low
   ["browser.tabs.unloadOnLowMemory", false],