What BitDefender appeared to say they were doing was providing browser plug-ins that wouuld scan the incoming SSL traffic after it had already been decrypted by the browser. So the browser handles all the SSL processes as usual. But avast! is already scanning the downloads with File System Shield when executed or opened, so may not be much value added ??? Not really scanning SSL traffic, just scanning the decrypted result before it is used by the browser for display or ?.
Maybe you could also do something like Avast! does with email. Set up your browser so it never encrypts anything, but just sends it along to avast! to do the scanning and then set up the SSL sessions and pass the encrypted traffic back and forth to the server, where encryption/decryption is actually done by a proxy using something like openSSL. But that sounds a lot more complicated than email, so ???