More than 2/3 of work on firebug is done by 1 mozilla employee, and there 2-3 other people we contribute to firebug from time to time. So it's pretty much in house.
IMO starting complete rewrite of firebug, in form of devtools, was very wrong. 2 years ago firebug was order of magnitude better than chrome devtools. Now it can't keep up with chrome. But firefox devtools only starts to become barely useful, If all that work have gone into improving firebug, Firefox would be ahead of chrome now.