Webmail works great in Firefox 3 beta 5 now. Mozilla must have fixed their CSS bugs.
Couple of tweaks if you login to webmail without toolbars… Type "about:config" in the address bar. Filter by "disable_window_open":
dom.disable_window_open_feature.location = false
dom.disable_window_open_feature.status = false
not sure what I mean by logging in without toolbars? Try adding this as a bookmark in Firefox…