Rebase TBB-Alpha to FF13.

https://developer.mozilla.org/en/Firefox_13_for_developers

Looks actually pretty benign to me, however, there's a ton of undocumented stuff in: http://beta.elchi3.de/doctracker/#list=fx&version=13.0

The most concerning titles seem to be: https://bugzilla.mozilla.org/show_bug.cgi?id=523304 https://bugzilla.mozilla.org/show_bug.cgi?id=731276 https://bugzilla.mozilla.org/show_bug.cgi?id=733335

This one might actually be an anti-fingerprinting enhancement: https://bugzilla.mozilla.org/show_bug.cgi?id=731276