Peter Eckersley of EFF writes:
Today EFF and the Tor Project are launching a public beta of a new Firefox extension called HTTPS Everywhere.
[…]
Firefox users can install HTTPS Everywhere by following this link.
As always, even if you’re at an HTTPS page, remember that unless Firefox displays a colored address bar and an unbroken lock icon in the bottom-right corner, the page is not completely encrypted and you may still be vulnerable to various forms of eavesdropping or hacking (in many cases, HTTPS Everywhere can’t prevent this because sites incorporate insecure third-party content).