MX-ONE "Weak Diffie-Hellman key"

This occurs with the self-generated SSL certificate on the Mitel MX-ONE v5.0. To access with Firefox:

Workaround for Firefox 39 and above:
1) In FireFox, enter "about:config" in the URL field and press enter.
2) Accept the "This might void your warranty!" warning :)
3) In the search field at the top, enter "security.ssl3.dhe_rsa_aes"
4) Double click each result (128 and 256) to toggle the Value to "false"

Now retry your site - it should work now. Remember to change these settings back when you're done.

Re-blogged from https://support.mozilla.org/en-US/questions/1066238