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.
Forgive me if I've completely misunderstood how GUIs work, but isn't reentrancy a basic requirement for GUIs in multi-threaded applications to be responsive when one thread of execution is blocked?
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.
