I make a lot of extensions, and I still don't know how the screening happens in the various stores. It's not working well, whatever it is. Part of the solution ought to require a submission in source format for easier screening, either by people or AI. (It can be obfuscated in-store if that's really what the developer wants.)
Mozilla and Opera require source code to be uploaded along with the extension, there is some human component involved in the review there. My understanding is that the human review got considerably less over time however. According to an email I received lately, Mozilla is reintroducing pre-publication review for popular extensions however.
I always thought it to be odd that Google doesn’t ask for extension source code, even when an extension is flagged for review. No idea what kind of review they can perform this way.
Back when I reviewed add-ons for Mozilla Add-ons, I did in fact verify that the source code produced the same build result as the extension submitted. Was tricky occasionally but usually worked well.
