[jamesgeck0]

I've definitely seen copies of desktop Firefox running malicious extensions. Mozilla somewhat discourages installing extensions that aren't on the official add-ons website (and thus haven't gone through an App-Store-like review process), but people do it anyway.

[kuschku]

And from the next version on, extensions installed from a non-accepted store are disabled and can’t be installed.

(Yes, as a developer, you can just add extensions, or as company, you can add your own certificate.