I think my problem is that I have script blocking but I'd rather deal with the logoffs than turn scripting back on.
 Guide to setting up ubuntu inside of virtualbox: http://www.psychocats.net/ubuntu/virtualbox
 Guide to using Firefox profiles: http://support.mozilla.com/en-US/kb/Managing%20profiles
(then modify your Firefox start menu or taskbar link or desktop link/shortcut and after the final double quote, add -no-remote -profilemanager
...that will let you easily start a new instance of firefox running a different profile even if another firefox instance is already running.