Does not happen with FF but with IE if you enter the chat with a name then start a new IE instance (not a new window) and you enter the same chat, you can be there twice or as many as you want. But you all knew aleady that you can enter a nick with IE and start FF and enter again with another, right?
I guess this cannot be fixed by only comparing IP and limiting to one... doing so would not make it possible for my girlfriend on her Mac on the same router to enter the chat at the same time as me? All computers behind a router got the same IP, right? BUT! I'm fine with an IP ban so if one funny guy is there 4 times with 4 nick then you can refuse his IP and alta vista!
I hope this can be fixed by a patch in 0.9.2 since I'm almost ready to launch our chat and have no plan to upgrade to 1.x as of yet. Or maybe if there is a log that is not history dependant and launch date is soon. But again with many new features introduced I may face lot of new bugs...