I hardened my MailNews email client by following some rules from the excellent Horloge Skynet Thunderbird-user.js: https://github.com/HorlogeSkynet/thunderbird-user.js/blob/master/user.js The disabling of some insecure ciphers is very interesting. Be careful not to disable javascript if you use OAuth2 authentication on your accounts. I hope it will be useful to some members of W. Enjoy.