For me, in Belenos, in my about:config for aBrowser I could only find these two of the three parameters you mention, and I toggled the two to false and went back to https://weakdh.org and got a clean bill of 'logjam health.' :)
security.ssl3.dhe_rsa_aes_128_sha;false security.ssl3.dhe_rsa_aes_256_sha;false Trisquel site seems to be working. I wonder if this would affect Evolution.