Unfortunately hoops aren't enough to fix this problem, because hoops generally involve some flag that you've gone through the hoop, and the installer can easily fake that.
Relatedly I did notice when putting my own addon through the signing process that there was a checkbox specifically for sideloaded addons, with the implication that the checks would be even more stringent. I'm not sure if that's enforced or not, or how.
I truly don’t understand why Mozilla is trying to do Microsoft’s job.
Never mind the entire idea of antivirus software is completely ridiculous from security PoV and basically a scam to have people pay for a false sense of security.
And... would Mozilla agree to sign it?
(Since, you know, the standard response over the years to users complaining about removed functionality in Firefox has been, "use an extension")