The ability to use extentions is one of the best parts of Firefox and I have several that I just can't do without now. Every once in a great while I'll run into something that doesn't work well with Firefox that I have to open up in IE, but those are very scarce now, and I can just use the "open in IE tab" extention to open them up in IE in Firefox. That way I don't have to deal with another browser window and I can still use my customized Firefox interface.