With reference to the project website, many sites on the web offer some limited support for encryption over HTTPS, but make it difficult to use. For instance, they may default to unencrypted HTTP, or fill encrypted pages with links that go back to the unencrypted site. The HTTPS Everywhere extension fixes these problems by rewriting all requests to these sites to HTTPS.
The version 0.9.0 of HTTPS Everywhere is a new beta version designed to offer improved protection against cookie-stealing extension Firesheep. Further, its development team has climed much better protection for Facebook, Twitter and Hotmail accounts, as well as completely new protection for bit.ly, Dropbox, Amazon AWS, Evernote, Cisco and Github.
More information about this project is available here.