Mozilla just released Firefox beta 5, the final beta beforr the browser’s expected June release date. There’s a new “thanks for helping test out Firefox” splash screen (pictued above). That weird Mac OS X jiff bug appears to have been fixed, too.
As always, full release notes can be found on the Firefox Web site.
I don’t know about the other versions, but the Vista version is definitely Vista-d up (in terms of looks, not reliability)