When visiting a website, it will or at least can track your history, such as which links you click, which pages you visit, what is your IP address, and so on.
Besides the website itself, your history may be also tracked by some other third parties, such as Google, if the website has used Google Analytics and/or Google AdSense.
So, how to check out if there is any third party tracking you when visiting a website? You can check out the Firefox add-on Collusion.
After installation, you will see the Collusion icon on the Add-on bar in the bottom-right corner of your Firefox browser, clicking on the icon, you can open a Collusion new tab, which will show you if the website you will have visited will pass your visiting history to any other third parties in a graph with circles.
As what you can see from the above image, when visiting Free Nuts, your history will be also tracked by the following 4 third parties:
- Quantserve.com (which is Guantcast.com now), and
But the above results were not 100% correct indeed, since the blog has used WordPress.com Stats, and your history should be also sent to WordPress.com, but which was missing in the graph. So, to get a better result, you'd better reset the graph to check out again.
Besides to reset graph, Collusion is also available for you to export graphs, but which I think is not useful, since you can't import them later.