While a good message that does have actual merit if you know what's happening already, I don't see how this is a legitimate consideration of MV3. The entire argument regarding security doesn't mention any of the reasons Chrome developers cite its security improvement, instead it brings up that Firefox "does good enough already" and that malicious extensions can still get past the review process. the review process is…
Installing random plugins is a security issue. But web tracking is by far the more significant threat.