probably, you misunderstand difference http:// and https:// proxy, there is no need for https:// to support https:// protocol between client and web server, HTTP proxy supports both http and https. https:// is required to encrypt traffic between proxy client and proxy with TLS. https:// is something rare and not natively supported by browsers, so 3proxy doesn't implement it currently. You can use something like stunnel to add TLS between proxy client and proxy.