Browsers with multi session support without tricks or gimmicks

I am looking for browsers with multi session support. Say one tab is an administrator logged into WordPress and the other tab is a member with only posting privileges.

Stainless has this on Mac and its perfect, but are there others? Say for Windows XP SP3 or Ubuntu Linux 10.04? I don’t want tricky stuff like loading Firefox with a command or having one Chrome session as admin and an incognito window as general member.

I find it convenient for development; but as a warning, like many browsers outside the big 5, huge sites like don’t load too fast or at all.