The Firefox Debugger is now maintained in Mozilla's central repository.
The Firefox Debugger was built in Github for the first 3 years of its development. Over 300+ volunteers contributed thousands of commits and built many of the features we take for granted today.
We hope to continue that spirit today in Mozilla Central. We believe the Debugger can be a great place to collaborate on the next iteration of developer tools. And, that everyone regardless of background or experience can contribute work of significance.