It's not clear to me how it is possible over https only sites without forging a certificate or MITMing the connection. The new content would have to be encrypte

It's not clear to me how it is possible over https only sites without forging a certificate or MITMing the connection. The new content would have to be encrypted with the correct key. If indeed this is possible then the internet is totally broken. "Reduce the effectiveness" implies that it is still possible though.