Issue #2805: skeleton for back out after fxa sign in

[severinrudie]

Checklist

• Confirm the acceptance criteria is fully satisfied in the issue(s) this PR will close
• Add thorough tests or an explanation of why it does not
• Add a CHANGELOG entry if applicable
• Add QA labels on the associated issue (not this PR; qa-ready or qa-notneeded)

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@2542639). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master    #2846   +/-   ##
=========================================
  Coverage          ?   51.26%           
  Complexity        ?      470           
=========================================
  Files             ?      122           
  Lines             ?     3507           
  Branches          ?      455           
=========================================
  Hits              ?     1798           
  Misses            ?     1561           
  Partials          ?      148

Impacted Files	Coverage Δ	Complexity Δ
...a/org/mozilla/tv/firefox/ext/WebBackForwardList.kt	0% <0%> (ø)	0 <0> (?)

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