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, 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.
Download HTTPS Everywhere from here: https://www.eff.org/https-everywhere