Rated 5 out of 5 stars
Contrary to what the reviewer bellow said, I found TJD very useful. TJD may not be as complete as Venkman (may he rest in peace) nor the built in FFX developer tools, but it provide one lean and mean UI and it's much faster and less bloated. Besides this plugin doesn't only target FFX. TJD can be also used for TB, SM, Komodo or any Xulrunner app.
In summary, whether you are an Add-ons developer, or one of the few remaining XUL Apps developers, you will be able to iterate and debug quickly using TJD.
I'm so glad I found this tool. Many thanks to the developer!