What you're asking for is not practical. If you want to block HTTPS, simply add a rule to block port 443. The problem is that you'll also block most major services that your users use (Google, Yahoo, Gmail, Microsoft, etc.). If you're concern over what your users are doing behind the HTTPS layer, simply setup an SSL proxy in pfSense. That way, the connection between the client and gateway will be secured, as well as the connection between the gateway and the website. However, the proxy will still allow you to see what's happening inside the HTTPS tunnel and thus block anything that you don't want the user to have access to.