Workaround for Firefox and Thunderbird: Disable DHE ciphers in the Zimbra Collaboration Server
Valid for Version 6.x and 7.x
On Server Store:
#su - zimbra
$zmprov mcf +zimbraSSLExcludeCipherSuites TLS_DHE_RSA_WITH_AES_128_CBC_SHA $zmprov mcf +zimbraSSLExcludeCipherSuites TLS_DHE_RSA_WITH_AES_256_CBC_SHA $zmprov mcf +zimbraSSLExcludeCipherSuites SSL_DHE_RSA_WITH_3DES_EDE_CBC_SHA $zmmailboxdctl restart