There is no state-changed:focus or focus event being fired when returning focus to Firefox. The problem was introduced into the 1/28 nightly build (1/27=good, 1/28=bad).
That's the date I suspected we broke it. It must be https://bugzilla.mozilla.org/show_bug.cgi?id=413778 which didn't properly fix that bug anyway.
Fixed by backing out fix for bug 413778.
Note for RelNote: People interested in testing Linux a11y should continue to test nightly builds instead of Beta 3. The process of getting the latest nightly build set up with the Orca screen reader can be found here: http://live.gnome.org/Orca/Firefox#preview.