As you browse the Web, Web sites watch you. Information is gathered about you, potentially shared with others, and possibly kept for a very long time. Which sites gather this information and which don't...and what do they do with the information? There's no practical way to know--unless you use TrackerWatcher, that is. This excellent, free Firefox add-on checks the privacy tracking features of Web sites you visit, and reports the results to you in great detail.
When you're on a site, click the TrackerWatcher icon, a new tab opens in Firefox with information about what the site tracks. You'll see four major areas: whether you are anonymous when you browse the site; whether the site shares information with others; whether the site gathers sensitive information about you based on your activities there, such as your race, religion, sexual preferences, and so on; and whether the site retains your personal information, and if so, for how long. Based on what you find, you may or may not want to keep browsing the site.
Note that when you install the TrackerWatcher add-on, its icon may not appear. If that's the case, right-click the navigation toolbar (the toolbar that contains the address bar and your navigation buttons), select Customize, look for the TrackerWatcher icon, and drag it to the right of your address bar. It should work then.