Any chance you could file bugs, particularly on the JS-related performance issues? I'm looking into some similar things right now, but seemingly JS-centric things seem to have a tendency to actually be from something else. It'd be nice to have something I could solidly blame on JS. If you file a bug with https://bugzilla.mozilla.org/enter_bug.cgi?product=Core&comp... and make it block bug 1299643, I'll see it.