Most of our computer usage these days is restricted to opening up a browser and going online. Since browsers are so commonly used they need to be protected
Say No to Scripts
NoScript addon for Firefox
Control your Cookies and more
Other useful and popular options include Ghostery (http://www.ghostery.com/) for both Firefox and Chrome that gives you a pop-up whenever you use an ad network or tracking script and allows to block the ones you don’t trust. Then there is Close ‘n’ Forget in Firefox, through which you can protect yourself from sites you’ve accidentally opened, only to realize later that you did not want it to appear in your history at all, you can simply press the icon and the site and all cookies related to it are permanently deleted. If the thought that all you visit or search on the net gives you the creeps, you should try out BetterPrivacy in Firefox, which blocks long term tracking by Google, YouTube, Ebay etc.
Sandboxie control panel