HTTPS Everywhere

HTTPS Everywhere is an add-on for Firefox & Chrome developed by the Electronic Frontier Foundation and The Tor Project. Once installed, it forces an encrypted connection with websites whenever possible. The advantages of this are that it helps prevent tampering with the packets sent to/from the website servers to your computer, as well as inhibiting others on the web from knowing what content you’re currently viewing. while it isn’t bullet-proof (most things rarely are), it will help prevent casual eavesdropping on your connection over public wi-fi and the internet at large, and should prevent man-in-the-middle spoofing attacks. The down side: if the NSA decides they need your records, https wont save you. Some of the websites it encrypts include Google, Facebook, Twitter, and hundreds of others, Firefox users can type "about:addons" in the address bar then select preferences under HTTPS Everywhere for a complete list.

The best part about this add-on? Install it, then forget about it, as it encrypts your connections automatically. 

You can Download HTTPS Everywhere here. For more information, see their FAQ.