How to include the CAcert root certificate in your browser

• If you get a message like the screenshot below, the CAcert.org root certificate is not included in your browser (it's included in GNU IceCat and Debian IceWeasel, among others). Gna! uses it to sign its SSL certificate, so let's do that; scroll down for the instructions.
  
  
• Go to to http://www.cacert.org/index.php?id=3 and click on "Root Certificate (PEM Format)":
  
  
  
• Accept the certificate:
  
  
  
• You now can browse Gna.org securely: