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.
We will continue to use Bugzilla, moz-phab, Phabricator, and Lando
Although we'll be hosting the repository on GitHub, our contribution workflow will remain unchanged and we will not be accepting Pull Requests at this time
We're still working through the planning stages, but we're expecting at least six months before the migration begins
Some amusing context (as a big Mercurial fan, myself):
According to the 2022 Stack Overflow Developer Survey, Mercurial is the 4th most popular response, beaten only by Git, Subversion, and "I don't use version control".
Git was roughly 94x as popular as Mercurial.
"I don't use version control." was a bit more than 4x as popular as Mercurial.
Unreal engine basically requires it for decent version control iirc. i had a nightmare trying to get git to work on my university project a few years back