From the website:

Collusion is an experimental add-on for Firefox and allows you to see all the third parties that are tracking your movements across the Web. It will show, in real time, how that data creates a spider-web of interaction between companies and other trackers.

I’ve shown the demo to several classes of mine at Washington University in St. Louis, & students are stunned. If this doesn’t make people wake up & install ad-blocking software, I honestly don’t know what will.