Mozilla has announced plans to migrate the primary code repository for its flagship Firefox browser from Mercurial to GitHub. The move is aimed at reducing the burden on development teams and modernizing Firefox’s contribution workflow.
In a post to the firefox-dev mailing list, Byron “Glob” Jones, Senior Engineering Manager at Mozilla, explained:
“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.”
The migration will take at least six months to begin, and once complete, Git will become the primary version control system, with Mercurial support eventually phased out. During the initial phase, Mozilla will maintain a one-way sync from Git to Mercurial to ensure continuity.
Why Move Away from Mercurial?
Mercurial is an open-source distributed version control system written in Python and licensed under the GNU GPL v2. Originally developed by Olivia Mackall in 2005 as a response to BitKeeper’s license changes, it was considered a strong alternative to Git. While Linus Torvalds ultimately chose Git for the Linux kernel, Mercurial gained adoption in other projects—including Firefox.
However, supporting both Git and Mercurial has proven to be resource-intensive. By consolidating around Git and hosting on GitHub, Mozilla hopes to reduce overhead and simplify the development process.
What Tools Will Stay?
Mozilla will continue to use a number of existing tools in the Firefox development workflow:
- Bugzilla for issue tracking
- Phabricator and moz-phab for code review
- Lando for automated patch landing
Despite GitHub’s built-in issue tracker and pull request tools, Mozilla plans to stick with its current setup for now. This decision ensures continuity for contributors familiar with the current workflow.
A Trade-Off: GitHub and Open Source Independence
While Git itself is open source, GitHub is a proprietary platform owned by Microsoft. This has raised concerns in the open-source community about long-term independence and platform lock-in. Some worry that relying too heavily on GitHub could pose future risks if its terms of service or pricing change.
That said, GitHub remains the de facto standard for open-source collaboration and offers robust infrastructure and tooling. Its wide adoption could help Mozilla attract new contributors—especially those already active on the platform.
“Going ‘all-in’ on GitHub means making Mozilla dependent on a Microsoft service that could change its conditions.”
Yet, Mozilla is no stranger to such trade-offs, having long relied on Google for a significant portion of its revenue via search partnerships.
Final Thoughts
This migration marks a major shift in Firefox’s development strategy and reflects the broader trend toward GitHub-centric workflows in open-source software. By streamlining its tooling and embracing platforms developers already use, Mozilla is betting on greater efficiency and contributor growth.
Stay tuned as the migration progresses—and if you’re a contributor, keep an eye out for updates on how this might affect your workflow.
