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.

What we are working on now for Collusion includes:

What do I do now? Usability improvements to help you take control of your browsing privacy.
Too much data, what does it mean? Visualization improvements for when the tracker graph grows unwieldy.
How does this compare to others? Anonymously share your tracker data with Mozilla so we can build a bigger picture of who is tracking what.
What are the trends? A public API from the tracker database for mashups, specialized visualizations, etc. Track whether a site gets more or less invasive over time, how your favourite sites fare, and much more.