I figure you guys have seen this already
But in case you are not up on your Firefox hacks, this lets you open Firefox in Firefox. Sounds wierd I know, but try it, you will see what I mean. Just copy and paste it into your address bar and hit go.
Just as a caveat, for the love of puppies dont open this in an IE (or probably a browser other than firefox) window. Bad things will happen, the sky will fall, there will be cats and dogs living together, it will be total anarchy.