There is a new Firefox extension in town and this one will encrypt your emails. The extension, called Freenigma, will encrypt your emails that you are sending using GMail, Yahoo Mail, or Hotmail. Right now the service is in a testing phase and you have to be invited to join, but you can sign up and maybe you will receive an invitation.
The extension is simple how it works. Once you have it installed you will see an “Encrypt” button in your email window. Once you press the button it will encrypt the message for you.
The biggest downside that I see right now is that the people receiving the email must also have a Freenigma account. When the person receives the message they simply have to decrypt the message by pressing the necessary button. They will then be prompted for their Freenigma account password and if it is correct the message will be displayed.
The browser itself is the one doing the encrypting/decrypting and it does not pass through any of the Freenigma servers. That means you will not be able to encrypt your attachments because a remote server would have to handle that. While this does sound like a great extension it would probably be nicer if the receiver of the email did not need to have a Freenigma account, but I guess beggers can’t be choosers.