Fix Settings/FxA-initiated browsing when offline

Per https://bugzilla.mozilla.org/show_bug.cgi?id=1082444 , attempting to browse the web from Firefox Accounts' sign-in/sign-up flow (by clicking on the PP/ToS) takes the user to broken screens. Here we restore a sensible flow.
And these are settings not prefs, so we may also want to change the name