This is a mirror that was being personally maintained, its been replaced by https://github.com/mozilla/gecko-dev, the maintainer sent an email saying the mirror was shutting down and people should move to the maintained version, this caused a bunch of traffic which caused github problems and they shut it down until they could fix it / bring it back up.
Seems like did a merge that somehow broke GitHub, and it's back to normal now.
(Don't forget, mozilla-central has more commits than GitHub can even count (they call it "10k+"), hundreds of forks, a few dozen commits a day, etc.. so it's atypical)
(Assuming the title hasn't been changed…) Removed from service isn't the same as disabled? To my mind they're synonymous. But I suppose the former may sound a little more inflammatory.
Interestingly, the initial email reported the cause to be a ToS violation.
Well, my train of thought is that disabled means it won't work for whatever period of time while removed means it won't work ever again because it's gone.
Dunno if its really news?