For one, phabricator is only used for code reviews, not for issue tracking which is managed by bugzilla. Github issues are nowhere near usable for a large product such as gecko/firefox.
note: IIRC Wikimedia had deprecated Bugzilla for bug reporting and replaced it by Phabricator.
> Github issues are nowhere near usable for a large product such as gecko/firefox
I have huge doubts about that.
Looking at the development of Servo on github was beautiful, the colored tags, the PR views, the activity stats, the reviews diffs, the wikis, everything about it was much more readable than it is on Bugzilla/phabricator IMHO.
https://github.com/servo/servo
The same can be said currently about webrender.
About scale, github is battletested, for Example Rust is an example of a large scale repo with a LOT of activity (~has more weekly commits than gecko-dev)
so the premise Github issues are nowhere near usable for a large product seems false.
What idiosyncrasies could mozilla devs have that are immutable and that make them so much different from large projects developped on github?
You specifically mention issues: Github can do meta-issues, can auto closes issues after PR merge, has bidirectional PR/issues references, can autoclose issues on markdown checklist check, etc etc
and if you couldn't fit into existing github features, I'm pretty sure you could totally solve your issues with Actions such as https://github.com/marketplace/actions/dependent-issues
Also github is accomodating, when the Apache foundation migrated to github they were open to do changes to the platform to facilitate Apache needs, cf: https://github.blog/2019-04-29-apache-joins-github-community...
In addition to my belief that github can be better or at least as good as buzilla, if gecko migrated to github, it would attract order of magnitudes more open source contributions because of the lower barrier to entry and to familiarity (also bugzilla is awful on smartphones)
You really think you should seriously consider the migration.
Last I looked github issues had no good way to express dependencies between issues, which is used a lot in gecko's bugzilla.
So you may be right, but I'm not a MoCo employee so I won't be part of any decision about that. Also consider the cost of moving all the tooling that exists to github (in the specific context of gecko): a migration needs to bring a lot of benefits, especially if you take into account that gecko's canonical repo is a mercurial one, not git.
Improving onboarding for new contributors would be nice for sure, but "order of magnitude more contributions" seems optimistic. I mostly expect there would be tons of low quality issues filed.
I would be very surprised if they did. The Firefox development workflow does not map very well onto Github.