On Monday, 27 February, Kevin Dangoor and I will be at Michigan State University to give a technical talk covering the new developer tools in Firefox. We will be meeting in room 1230 of the Engineering Building at 6pm.
There has been a lot of work on native developer tools for Firefox, along with adding more capabilities and speeding up Firebug. Starting in Firefox 10, the Inspector and Scratchpad were released. In the next versions of Firefox, users can find a native JavaScript debugger, CSS style editor, and more.