According to [0], Mozilla requires all extensions to have a source in human-readable format and runs a test suite on them. They mention "code review" there, but don't say whether it's manual or automatic. I'd love to hear about it from someone who has some experience with the process.

[0] https://extensionworkshop.com/documentation/publish/submitti...

For my extension the review was automatic, and flags things like direct html editing. I only have a few hundred users though, so I'm not sure at what point they decide to do manual reviews.

Mozilla runs an automatic check on all extension versions before they get published, and Recommended extensions also go through a manual review before publication.

Listings which do not participate in the Recommended extensions program may also get a manual review after they were published, but immediate human review is not guaranteed.

If you're a developer, I'd recommend disabling automatic extension updates in Firefox, and configuring a script to get notified about updates, even if you only use Recommended extensions.

Extension source viewer is excellent for reviewing updates yourself before installing, and it is maintained by Rob Wu, an engineer at Mozilla.

https://addons.mozilla.org/en-US/firefox/addon/crxviewer/