If you are using thunderbird to connect to a mail server, and you see an error like this:
Error: An error occurred during a connection to host.server.com:993.
SSL received a weak ephemeral Diffie-Hellman key in Server Key Exchange handshake message.
(Error code: ssl_error_weak_server_ephemeral_dh_key)
Then this indicates the server is vulnerable to logjam attack, and should be fixed right away. If you check over on https://weakdh.org/ then you’ll see how this can be fixed. But basically, you need to disable support for export cipher suites and generate a unique 2048-bit Diffie-Hellman group.
If you are not the owner of the server in question, then you should contact the server owner, and have them do this. If you can not reach them, there is a work around.
1. Click on Tools -> Options -> Advanced
2. Click on Config Editor
3. search for following keys and set them to false
Restart thunderbird, and you should be all set.