A less confusing title would be “Mozilla drops support for Mercurial (...)
It's not even about GitHub at all. Taken straight out of the announcement:
“For a long time Firefox Desktop development has supported both Mercurial and Git users. This dual SCM requirement places a significant burden on teams which are already stretched thin in parts. We have made the decision to move Firefox development to Git.”
Was this thing generated by a poorly trained LLM?