A very topical question! Did you have an alternative in mind?

There is much work progressing via Participation Systems which has been integrating a number of approaches to identity access management the last year. It’s my view, that Github was one of the first of these as we could use Oauth and hardware 2FA devices like Yubikeys. Solved a lot of issues quickly. We could not have known about Microsoft’s inention for this acquisition, and I do not currently know Mozilla’s official position on this.

Please understand that ParSys team is busy rolling out a number of alternatives in an IAM roadmap. Things like: staff and volunteer contact information is merging into the one tool, and integrating a more useful Firefox accounts identity. I asked about 2FA/U2F in bug 1464888 specifically in the Firefox Accounts so we had other options than Github.