OC 9 + mint 18.1 can't use https

things have improved compared to the previeous post.
In the first place, the port 443 was closed. I had to open it with the command: sudo nc -lk 443; second, compared with the open door, firefox not you tell me more "unable to connect" but "secure connection failed" which I consider a step forward.
The only little thing that is missing is the option represented by the button "advanced", down which I could accept the certificate so that you can also use https.
Now I just need to find out why firefox does not communicate to me, "your connection is not secure" and not present to me the buttons: go back or advanced.

You can use the ssl test on ssllabs.com, it can tell you what is wrong with your certificates, ciphers, ....