So long Firebug. It was like Christmas when we first saw what you did for us.
And as a slight nitpick, the IE Dev toolbar came out about 6 months before Firebug and as best I can remember actually had more functionality than Firebug for quite a while.
It's some sort of persistent web developer myth that Firebug came first. Firebug was just easier to find/install, you had to know that the IE6 developer toolbar existed.
NB: I hate IE as much as the next web dev, but credit where credit's due...