I seem to be on a theme lately... I found a free add on that not only can block tracking sites, but can show you which company is tracking you on each web page you visit. It's called Ghostery, at www.ghostery.com. There's a little Pacman-like ghost at the top of your screen that shows you the number of tracking sites attempting to follow your surfing. You can click on that and it shows you which sites they are. (Google seems to be very interested in all that we do.) You can choose to block all, none or some of the sites. It works with Firefox, Chrome, IE and Safari.

I am not associated with the company, btw.