It will encrypt your communications with a number of major websites such as Facebook, Twitter, Google Search, Wikipedia, PayPal, NYT, etc. and ensures your security.
Why this extension? For example, some websites like Facebook offer some limited support for encryption over HTTPS, but make it tough to use.
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 troubles by rewriting all requests to these sites to HTTPS. Firefox users can download this extension (currently it is a beta product) at source.
