Encrypt the Web! Automatically use HTTPS security on many sites.
HTTPS Everywhere is an extension created by EFF and the Tor Project which automatically switches thousands of sites from insecure "http" to secure "https". It will protect you against many forms of surveillance and account hijacking, and some forms of censorship.
Source code and bug tracker are available at https://github.com/efforg/https-everywhere. **Please do not submit bug reports in the reviews!** (I can't respond to them there.)
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If HTTPS Everywhere causes a site to look weird or break, you can disable it for that site using the button in the address bar in the top right of your screen. HTTPS Everywhere for Chrome is currently in beta, and a few such issues are inevitable due to bugs in websites' HTTPS support. Also watch for a "shield" button in the address bar, which means that Chrome blocked insecure portions of the page. Sometimes pages will look weird with their insecure portions removed. Clicking on the shield will let you load them, but will reduce your security and privacy.
Special thanks to Aaron Swartz, Mike Perry, Jay Weisskopf, Nick Semenkovich, Jacob Hoffman-Andrews, Yan Zhu, Vijay P., and William Budington for their work on the Chrome port.