Read article here from the Electronic Frontier Foundation website.
HTTPS Everywhere Updates Web-Surfing Security
HTTPS secures web browsing by encrypting both requests from your browser to websites and the resulting pages that are displayed. Without HTTPS, your online reading habits and activities are vulnerable to eavesdropping, and your accounts are vulnerable to hijacking.
This new version of HTTPS Everywhere responds to growing concerns about website vulnerability in the wake of Firesheep, an attack tool that could enable an eavesdropper on a network to take over another user's web accounts -- on social networking sites or webmail systems, for example -- if the browser's connection to the web application either does not use cryptography or does not use it thoroughly enough. Firesheep, which was released in October as a demonstration of a vulnerability that computer security experts have known about for years, sparked a flurry of media attention.
To download HTTPS Everywhere for Firefox:
https://www.eff.org/https-everywhere
For more on implementing HTTPS in websites:
https://www.eff.org/pages/how-deploy-https-correctly