It really feels like Firefox is not a supported browser on GitHub, I hit this and also find that much of the time the commit message is not correctly pulled from the PR description when that setting is enabled
to be fair, git itself only supports sha256 (as opposed to all of sha2) and even then it's marked "THIS OPTION IS EXPERIMENTAL" so many are afraid to use it
ff merge support though....what a world that would be
i had something similar with PRs last year. 2x PRs of mine disappeared for me. they were still counted in the total number of PRs and everyone else could see them.