Try different way to disable Firefox 'welcome pages' (mkaply)
    
    Thanks to Mike Kaply in
    https://bugzilla.mozilla.org/show_bug.cgi?id=1703903#c18 , this
    should avoid Quick Suggest onboarding, "Total Cookie Protection"
    onboarding, and future annoying things using the same mechanisms
    without using the prefs mechanism or going after each one case
    by case.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>