Websites
For encrypting WWW/HTTP connections, typically HTTPS is used. This can also be used for opportunistic website encryption. Most browsers verify the webserver's identity to make sure that an SSL certificate is signed by a trusted certificate authority. The easiest way to enable opportunistic website encryption is by using self-signed certificates, but this causes browsers to display a warning each time the website is visited unless the user imports the website's certificate into their browser.
There are add-ons for Firefox called HTTPS Everywhere by EFF and HTTPSfinder. These addons find and automatically switch the connection to HTTPS when possible.
Read more about this topic: Opportunistic Encryption