This is my understanding from reading the docs just now:

You submit patches to Phabricator, not to GitHub.

https://firefox-source-docs.mozilla.org/contributing/contrib...

> To submit a patch for review, we use a tool called moz-phab.

That does mean you need an account on Phabricator, but not on GitHub https://moz-conduit.readthedocs.io/en/latest/phabricator-use...