HTTPS Everywhere is designed to create secure HTTPS connections with some of the more popular sites on the Web. It s not meant as a cure-all for the myriad man-in-the-middle and eavesdropping attacks that plague Web communications, but helps lock down the traffic to these sites. Not all of the traffic will be encrypted because they include content from third-party sites that’s insecure. The extension, which is only available for Mozilla Firefox, is available on the EFF site.
Source: https://threatpost.com/eff-and-tor-launch-https-everywhere-firefox-extension-061810/74123/