[moontear]

Without knowing their reason, there are a few things tied to the org where multiple orgs make sense. If you do SSO for example you tie the org to a SSO provider, you can’t tie „just a few users“ to the SSO provider (afaik). The Firefox repo may have totally different authentication / users than the main Mozilla repo.

[pornel]

The GitHub SSO is annoying. I can't even view public issues if I'm logged in to GitHub, but haven't recently re-authenticated with SSO.

GitHub also has a lot of features and authentication scopes tied to the whole org, which is pretty risky for an org as large as Mozilla.