HTTPS Everywhere is a web browser extension that promotes the use of encryption wherever possible. It is a Firefox, Chrome, and Opera extension that encrypts your communications with many major websites, making your browsing more secure.
HTTPS Everywhere is produced as a collaboration between The Tor Project and the Electronic Frontier Foundation. Many sites on the web offer some limited support for encryption over HTTPS protocol, 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 using a clever technology to rewrite requests to these sites to HTTPS.
Questions and Caveats
Sadly, many sites still include a lot of content from third party domains that is not available over HTTPS. As always, if the browser's lock icon is broken or carries an exclamation mark, you may remain vulnerable to some adversaries that use active attacks or traffic analysis. However, the effort that would be required to eavesdrop on your browsing should still be usefully increased. Update: in recent versions of Firefox, Mozilla has removed the broken padlock indicator. Now, the only difference between a secure and insecure HTTPS deployment is the blue or green tint on the left of the address bar for secure deployments
Answers to common questions may be on the asked questions page.
HTTPS Everywhere can protect you only when you're using sites that support HTTPS and for which HTTPS Everywhere include a . If sites you use don't support HTTPS, ask the site operators to add it; only the site operator is able to enable HTTPS. There is more information and instruction on how server operators can do that in the EFF article to Deploy HTTPS Correctly.