Since the 30th of June of 2015, Mozilla Firefox doesn’t support connections to a server with weak Diffie-Hellman ciphers anymore (Mozilla Release Notes🙂
Perform at your own risk. Accidental adjustment may effect Firefox’s performance. To fix type about:config in your Firefox web browser, in the address bar. Change the next settings with the next values:security.ssl3.dhe_rsa_aes_128_sha=false security.ssl3.dhe_rsa_aes_256_sha=false
The values should be true by default. Click on them to change to “false.”
Now your Cisco Unified Communications Manager is accessible.