Fix conflicts in mobile onbarding while rebasing to esr68.2.0
It turns out that there are a number of conflicts between our mobile onboarding code and the coming esr68.2.0 which we need to think about how to resolve. They stem in particular from
https://bugzilla.mozilla.org/show_bug.cgi?id=1570878
and
https://bugzilla.mozilla.org/show_bug.cgi?id=1587631
Not sure whether we want to just back out those changes or make them otherwise compatible with our modifications.
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