These are the three browser plugins for device protection I recommend you install. The first one is arguably more important than anti-virus, and takes a while to get used too as you have to enable scripts on pages you trust.
This is an updated post from April 2012 post called the browser tracker test. An important caveat before installing any browser plugin, is that if you read the warnings from your browser, it is likely that the developer of that plugin will have access to every website you ever visit while having that plugin enabled! That being said, if you’re going to install plugins to improve your privacy and security while browsing, these are the top 3 recommended browser plugins for 2013: