To protect users from cryptographic attacks that can compromise secure web connections, the popular Firefox browser will block access to HTTPS servers that use weak Diffie-Hellman keys.
Diffie-Hellman is a key exchange protocol that is slowly replacing the widely used RSA key agreement for the TLS (Transport Layer Security) protocol. Unlike RSA, Diffie-Hellman can be used with TLS’s ephemeral modes, which provide forward secrecy — a property that prevents the decryption of previously captured traffic if the key is cracked at a later time.
