Firefox has automated "malware checking" for extensions, the Mozilla AMO Validator, and it's been basically torn to pieces by the community for being not actually secure [1] plus a major hassle for developers [2], to the point that large extensions with hundreds of thousands of users have stopped using the official Firefox extensions repository.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1227867#c2
[2] https://forums.zotero.org/discussion/28847/zotero-addon-is-n...