Earlier quoted context omitted.
Did they make Firefox re-entrant so that a f'd up page in one tab doesn't affect all the other ones and the browser chrome?
Either you're incredibly involved in the Mozilla codebase, or you're misusing the word "re-entrant" [1]. Since you're asking about development status, I'm going to assume the latter. [1] http://en.wikipedia.org/wiki/Reentrant_(subroutine)
I mean, I guess they could use a message queue between their thread for window chrome and page rendering, but I don't recall them ever mentioning anything about that in any dev journals that I used to read years ago.