Firefox: Error code: ssl_error_weak_server_ephemeral_dh_key

Starting with Firefox v39 you will receive the following errors when accessing secure websites with a weak ephemeral Diffie-Hellman key:

An error occurred during a connection to helios.alt-itc.ca:8443. SSL received a weak ephemeral Diffie-Hellman key in Server Key Exchange handshake message. (Error code: ssl_error_weak_server_ephemeral_dh_key)

How to resolve this:

1) Ask the webmaster to correct this on the server side (if you have such an option).

2) Perform the following:

i) In the address field of Firefox, type in: 

about:config

ii) Click "I'll be careful, I promise"

iii) Find the following keys (type this into the search field):

security.ssl3.dhe_rsa_aes_128_sha

Click on "true" under "Value" to make it "false"

Find the next key:

security.ssl3.dhe_rsa_aes_256_sha

Click on "true" under "Value" to make it "false"

close the window and you're done. You should be able to refresh the page that was not connecting. No need to restart Firefox.