You can find that information on the security tab of your browser's developer tools. You can also find a lot more info about any site's HTTPS configuration at ssllabs.com. Here's the report for lists.gnu.org: https://www.ssllabs.com/ssltest/analyze.html?d=lists.gnu.org
A good first step is disabling SSL 3.x and TLS 1.0 in your daily browser. I would also recommend the excellent Qualys SSL Server Test: https://www.ssllabs.com/ssltest/
