What They Know. “What third-party sites know about you will be shown in the results of running the script. The results will present you with a list of sites your browser has visited … For each site on this list we report which third-parties have knowledge of your visit to this site. We also predict your age and gender based on demographic information for users of these sites, as well as your location…”
Be ready to be surprised. This site also offers some suggestions on how to increase your privacy.