Bug 1071259 - Clear the loop.hawk-session-token.fxa pref on shutdown to workaround bug 1071247. r=jaws

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extra : rebase_source : 49df694bae7a03d07552a47615b2711d076b8f43
Bug 1065144 - Unhide Loop Firefox Account UI. r=standard8

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extra : rebase_source : 4f22f916201958f52d9bbbdb064641239da2277d