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…

javascript:window.open(‘https://beta.mailtrust.com/mailbeta/login.php?user_name=EMAIL&password=PASSWORD’,’Webmail’,’toolbars=0,resizable=1,left=0,top=0,width=1000,height=750′)