Category: Firefox

Firefox 39.0 SSL Error: Weak Ephemeral Diffie-Hellman key

Recently updated Firefox to version 39.0 and tried to access Call Manager and Contact Center Express. Got the following Firefox error:

SSL received a weak ephemeral Diffie-Hellman key in Server Key Exchange handshake message. (Error code: ssl_error_weak_server_ephemeral_dh_key)

Solution documented in


  1. In Firefox, Enter “about:config” in the URL field and press enter.
  2. Accept the “This might void your warranty!” warning by clicking “I’ll be careful, I promise!” button.
  3. In the search field, enter “security.ssl3.dhe_rsa_aes”.
  4. Double click each result (128 SHA and 256 SHA) to toggle the Value to “false”.

No need to close and reopen the browser.