In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful
* In the search box above the list, type or paste ssl3 and pause while the list is filtered
(3) Double-click the security.ssl3.dhe_rsa_aes_128_sha preference to switch it from true to false (this usually would be the first item on the list)
(4) Double-click the security.ssl3.dhe_rsa_aes_256_sha preference to switch it from true to false (this usually would be the second item on the list)
That’s it, you can test using: https://www.ssllabs.com/ssltest/viewMyClient.html