Created by EFF and Tor, HTTPS Everywhere is a Firefox and Chrome extension that encrypts your communications with many major websites, making your browsing more secure.
Download the software for free here: https://www.eff.org/https-everywhere
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.
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.
Answers to common questions may be on the frequently asked questions page.
HTTPS Everywhere can protect you only when you’re using sites that support HTTPS and for which HTTPS Everywhere includes rules. 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 How to Deploy HTTPS Correctly.
Read more about this and download the software for free here: https://www.eff.org/https-everywhere