Bug 905637 wip

I'm a bit stuck, it seems like FxAccountsIACHelper.sendMessage is failing when it calls `app.connect` at line 46.

At least, that's where the nightly debugger seems to lose the thread--the app.connect.then promise is never executed.

I am not blocked by this, I can wire up the logged-in UI by stubbing out the user data, but it'd be good to get feedback from @ferjm or @sampenrose on this bug.