Find out how web sites are watching you with Ghostery
The alert bubble disappears after about 15 seconds. Or if you'd rather not see the pop up every time you visit a new web site, you can right click on the Ghostery icon in the Firefox status bar and suspend the service until you want to use it again.
Not every item that's classified as a "web bug" is necessarily malicious. In fact, most are simply the tools that web publishers use to place advertising on their site, or enable other features like third party commenting system Disqus. But normally many of these scripts are hidden. And if you want to know what kind of scripts on any web page are tracking you, Ghostery can help you find out.