If you use Chrome or Firefox, this is one of the most important extensions you can install. Many sites offer secure connections, but don't always make that clear. This extension will encrypt as much of your web traffic as possible. This is especially important if you use public WiFi a lot in coffee shops, restaurants, and other places.

HTTPS Everywhere Keeps Your Personal Information Safe on Over 1,400 Sites, Available for Firefox and
Chrome/Firefox: HTTPS Everywhere is a simple extension that, with just a one-click installation, can seriously increase your security on over 1,400 web sites by encrypting your connection.