Encrypted Communications is an add-on for Firefox that encrypts messages to be transmitted in a confidential way, mainly to send E-Mails with sensitive data, or to post on Facebook or any other social network confidentially. If you need to send a secret, this add-on will help.
Here is more about the add-on from the developers:
This add-on can be used to transmit messages in a confidential way by encrypting them before they are actually sent. It works by catching the contents of a Form’s TEXTAREA or other editable elements, you just have to RMB over it and click on “Encrypt Communication”.
The add-on works great. The only problem I can see is that the person you are sending the message to will also need to have this add-on installed.Want to learn more? You can pick up Encrypted Communication from the Firefox Add-ons website.