Firefox has moved onto Github

That's a read-only mirror, not a "move onto GitHub".
PRs get automatically closed, referring to the contrib docs.
https://firefox-source-docs.mozilla.org/contributing/how_to_submit_a_patch.html
https://phabricator.services.mozilla.com/
- It looks like the main repository. The "How to submit a patch" mentions even the github repository. Even though it does not accept pull requests it seems to be not just a mirror.
  
  When I searched for text "github" I did not find anything. But searching in the inspector to cover urls:
  Firefox and related code is stored in our git repository.
  Which makes it all the more confusing. Stored there, but patches only elsewhere?
  Really, for a "moved their sources" claim I'd prefer some form of announcement or docs that describe this.
- I was about to reply with a "oh, really? Whoops, I maybe should I have looked a little deeper" and edited for the post title, but I'm not so sure, looking into the first link you posted.
  RE: phabricator...I don't know what that service is or is for, so I can't comment if there's any proof therein.
  But the "how to submit a patch" page linked has a section that seems to at least suggest that their Github repo is now first-class, per the first line of the section.
  
  Phabricator was an alternative for a development platform of sorts; development ceased in 2021. They're still running here and there, but I expect them to be in the process of being deprecated.
  
  RE: phabricator…I don’t know what that service is or is for, so I can’t comment if there’s any proof therein.
  The how to submit a patch section documents that that's where they accept patches. And they do their reviews and change iterations there. By necessity, that also means hosting/having the repos.
  That's confusing to me.
  They only accept patches on Phabricator, have the sources there, but suggest using GitHub, but afterwards Phabricator to submit the changes?
  I can only imagine it's to lower barrier to entry because GitHub is more well known. But this just seems like a confusing mess to me, without clear wording of intentions and separation of concerns [in their docs, not your post or comment here].

That's very good. Once I wanted to compile Firefox myself for some reason I no longer remember, but their Mercurial-based system was a hassle to work with. Most of us are already familiar with git. So, I know I'm going to be more inclined to make code contributions now that it uses git.
Just wish they could've chosen another git-based option like Codeberg, or even an internally-hosted server. I'm rather wary of GitHub/Microsoft swallowing up so many open source projects.
- Inertia's a bitch, and they started before git existed. It was a dark time.
- Seems that they're not accepting pull-requests via GitHub, which is a bit of shame.
  
  For a complicated project I get it, github's PR system is kind of bad (horrible branch based workflow and no stacked diff support resulting in increased churn) compared to the alternatives.
  That's why we have tools like Graphite to add stacked diff support on top of github, and other devs creating new VCSs because git still hasn't made it's interactive rebase and merge conflicts easy enough to handle for juniors and it should be simpler.

It's sad that an entity the importance and the size of Mozilla chose GitHub over self-hosting. It's insane they were still using Mercurial in 2025.
- They aren't moving, it's a code mirror. Everyone seems to be misreporting this. There's a GitHub action to auto close PRs.
  
  It's not a mirror. It's the primary repository. And yes unfortunately they aren't accepting PRs or using it for issue tracking, but it's a start.
- It’s insane they were still using Mercurial in 2025.
  What?
  
  What what? Mercurial is dead. Not even Facebook use it any more.

Bc this seems to be a crosspost, imma cross-comment:
I get wanting to phase out Mercurial in favour of git. But why did they have to choose Github T_T
Ideally they would have just hosted a their own Forgejo instance (heck, a Gitlab one would have been better too FFS). Even just using Codeberg and donating would have been better
The for-profit side of Mozilla seems to have succeeded in purging most of the principles Mozilla used to have (IK they have been eroding over the years and sometimes been too "pragmatic", this is just the cherry on top of a long series of shitpiles)
If Mozilla actually stood for a free/libre future they'd push Forgejo to the lvl they need it to be (if it already isn't capable of all that stuff. Haven't rly interacted much with it). Since they will still keep the CI/CD on Mercurial for now, there is even less valid reasons for using Github...
https://programming.dev/comment/16918830
- Mozilla is just a mouthpiece nowadays. Google money goes in, bullshit comes out. They are only around to accept Google money and to do so, they don't have to actually compete, they just have to be bigger than the alternatives.
  If they self hosted a git forge, that would mean paying less money to some "thought leader" and we all know they can't have that!
  Anti Commercial-AI license
  
  I personally wouldn't go that far tbh, but I haven't rly looked into it that much so idk.
  To me it seems like they are still maintaining Firefox, Gecko, and Thunderbird (which is more independent tho IIRC) quite well.
  I use Thunderbird directly and Firefox through Librewolf
  (haven't rly had the drive to look into Thunderbird analogues to Librewolf. Should rly do that tho)

But why?
- Because Mozilla is the master of bad ideas and most open source projects are leaving github, not joining it.
- I would guess Mozilla is making plans for what happens when Chrome is sold. Now that Firefox has proven to be an inadequate antitrust shield for Chrome, there is no longer any reason for Google to continue funding them.
  
  how does moving to github help them if chrome is sold?
- They're switching their main repository from Mercurial to Git. Mozilla started using Mercurial before Git became de facto standard, but I imagine these days learning Mercurial is seen as an unnecessary obstacle for new contributors, hence the current switch.
  As for why GitHub specifically, it's because that's where the rest of Mozilla's projects already are. They have been using GitHub for a long time (14 years or more), with thousands of repositories there. It's why Rust and Servo are on GitHub, for example.
  Edit: See https://glandium.org/blog/?p=4346 for more thorough/accurate info.

Also a devclass post Mozilla quietly makes Microsoft’s GitHub the authoritative home for Firefox code suggests FF is making the GH repo the place to go as the source of truth for FF, :( This move to me is really sad, instead of moving to FLOSS alternatives it's preferring a proprietary with a terrible hosting licensing (gitlab one is much better for example, not sure about codeberg's one, but for sure is better as well), and what's worse, one that uses anything hosted in there for its own purposes, including feeding openAI stuff with FLOSS code violating any licenses and so forth. Which actually makes me strengthen the idea that mozilla is trending to go in the wrong direction making things worse on every step they follow.
I use a derivative, Librewolf, but in the end it depends on the FF code... Sadly, using GH is still like the norm, and I can change that. servo browser engine and verso (browser based on servo) are also hosted on GH. But at least they started there and migrating is always a hard decision, FF is just moving there having other options, so it means they don't care about GH mistreating users code...