Developer Assistant
Developer Assistant is an add-on for Firefox which offers tools of convenience to developers.
Developer Assistant was originally called Extension Developer Extension and was created by Ted Mielczarek, with code contributed by Jesse Ruderman, Cüneyt Yilmaz, Tony Chang, Gavin Sharp, Cesar Oliveira, Nickolay Ponomarev, and Brett Zamir.
With Ted no longer actively maintaining the project, Brett Zamir accepted to take over the project (though he is not able to devote very much time to it and is focusing on web developer components more than extension developer components--thus the renaming of the extension).