I use Firefox at home sometimes. Using it at work is very annoying because it does not support NTLM authentication. For those who don't know what that is - basically Firefox will always ask you for your network userid/password when you browse your company's intranet. IE uses your network login automatically since you are already logged in on your PC, so you don't have to type it everytime you need to borwse your intranet. I think even Netscape supports NTLM - but I am not sure.. I haven't used Netscape for ages. Why Firefox did not implement this feature is beyond me. Also, it is a little slower then IE but that's expected since IE is very tightly integrated with the OS. Other then that, it is a great alternative and the tab interface is awesome - something that IE should've done a long time ago.