[ajayyy]

Mozilla reviewers do very detailed reviews. Unlike Chrome, they sometimes do manual reviews, looking for potential XSS or similar problems, and will let you know the exact line causing it. The Chrome web store is almost unmoderated though.

[krono]

There's plenty of proof to the contrary for the majority of extensions, including their recommended ones.

See this article (not by myself) and comment thread from two weeks ago for further details:

https://www.coloursofosint.com/posts/Investigating-Firefox/

https://news.ycombinator.com/item?id=37125402

[chatmasta]

Do they review every update?

[elashri]

Yea, and they do that for recommended extensions on the Firefox store only. It does not apply to all extensions