Up to now, Mozilla has been supporting the use of both Git and Mercurial DVCSes by its contributors <https://devclass.com/2023/11/07/mozilla-will-move-firefox-development-from-mercurial-to-microsofts-github/>. But no more: it is giving up on Mercurial, and making things exclusively Git-based. Furthermore, it is moving to use GitHub for hosting its repos. I can remember the discussion over which distributed VCS they should switch to about a decade ago, back when I was new to Git myself. Even then, the momentum was clearly on the side of Git. However, the Mozilla crew wanted something that would work well on Windows, not just on Linux, and back then the process-heavy execution model of Git gave poor performance on Windows. Hence they went for Mercurial. Presumably that objection no longer applies; suitable compromises have been made in the architecture of Git to cater for the platform that thinks 26 drive letters ought to be enough for anybody. (I can’t remember what Mozilla were using before that; probably Subversion.) Using GitHub, on the other hand, seems in some ways like a step backwards for distributed development. Linus Torvalds famously pilloried their lame pull-request system <https://github.com/torvalds/linux/pull/17#issuecomment-5654674>, which just happens to be the one feature of your GitHub repos that you cannot turn off.