It was a guess and I never claimed it was 100% correct, and I'm happy to stand corrected. No hard feelings there.

If the CI/CD is the most intensive part, it seems reasonable to move all of the other parts to a free provider to focus on the part that would be harder and more expensive to move. Even if they don't ever move any of the CI/CD over, I feel like I can understand the rationale for reducing the scope to just that rather than the source hosting. I've worked on plenty of projects with way less traffic than Firefox over the years that used GitHub for source hosting but alternate CI/CD; GitHub didn't even have built in CI for a while, so that was the only way to use it.

Given the frequency I see comments on this site about Mozilla trying to do far too much rather than just focusing their efforts on core stuff like Firefox, I'm honestly a bit surprised that there aren't more people agreeing with this decision. Even with the other issues I have with Mozilla lately (like the whole debacle over the privacy policy changes and the extremely bizarre follow-up about what the definition of "selling user data" is), I don't see it as hypocritical to use GitHub while maintaining a stance that open solutions are better than closed ones because I think trying to make an open browser in the current era is a large and complicated goal for it to be worth it to set a high bar for taking on additional fights. Insisting on spending effort on maintaining their own version control servers feels like a effort that they don't need to be taking on right now, and I'd much rather than Mozilla pick their battles carefully like this more often than less. Trying to fight for more open source hosting at this point is a large enough battle that maybe it would make more sense for a separate organization focused on that to be leading the front in that regard; providing an alternative to Chrome is a big enough struggle that it's not crazy for them to decide that GitHub's dominance has to be someone else's problem.

I think it can be done half/half. Do some, well-defined builds at GitHub and pull in for testing. Another comment tells that some users needed 10+ minutes to get a lock to pass their tests through CI, so maybe some sanity tests can be offloaded to GitHub actions.

I'm not claiming that my comment was 100% accurate, but they plan to move some of the CI to GitHub, at least.