David Cancel just created a wonderful privacy enhancing technology for Firefox---up there with Ad Blocker Plus in my view. In a simple and straightforward way, Ghostery reveals who is tracking your views of a page on the Internet according to a common but under-examined method: web bugs.
As David explains, "[w]eb bugs are used to track your behavior on the web in order to help the sites you visit to understand their own audiences and to allow advertisers to target ads at you." To expand a little, web bugs are tiny (generally one-pixel) pictures on a web page that tell a host or third-party when and by whom they are being loaded, which in turn reveals that the page itself has been loaded. David's elegant plug-in "scans the web pages you visit to find web bugs" and displays their owners in the upper right hand corner of the page. Ghostery is easy to install, use, and shut off.
Ghostery represents an important development. Although we can sort of opt out of cookie-based tracking by third-party advertising networks, we have a very poor handle on web bugs. (I say "sort of" because in some instances you're not opting out of tracking in the sense of stopping the advertisers from recording whether you've visited a particular page, but only out of being served targeted ads. A discussion of this unfortunate reality here.) David's new privacy enhancing technology helps shore up a major privacy issue on the web. Thanks David!