If you go here:- http://www.mozilla.org/
The 0.9RC is there as well as the 0.8 Haven't tried the 0.9RC yet myself, been using 0.8 for ages. Haven't taken a look at Thunderbird myself yet, will have to take a peek at some point.
yeah, what improvements does 0.9rc have over 0.8? i noticed 0.8 doesn't like some CSS/shtml in pages, not sure if that will be fixed, its not *that* major but yes... it does kick the **** out of IE