monitors content from third parties that frequently appears on other sites (something that often, but not always, signals a tracker) and either blocks such content by default or allows you to select it for blocking. Click on Safety, InPrivate Filtering to enable it. You'll need to enable each time you start the browser.

Firefox users can try a wide array of privacy-protecting add-ons. BetterPrivacy gets rid of Flash cookies, which some advertisers use and normally can't be deleted. creates behavioral-advertising opt-out cookies (the good kind) that will stick around even if you get rid of your other cookies. CookieSafe allows for fine-grained management of all cookies.

The excellent add-on alerts you to hidden trackers but doesn't stop them. To block common JavaScript trackers, you can use . Keep in mind that while the other add-ons mentioned above won't significantly change your browsing habits, NoScript will, as it prevents many sites from working properly until you manually approve them.

One option is to set NoScript to allow all JavaScript, and then, when Ghostery reports a tracker, right-click on the NoScript icon to set the tracker source (which Ghostery also reports) as untrusted. Allowing all JavaScript nullifies NoScript's protection against potential JavaScript attacks from unknown sites, but it means far less hassle in your day-to-day browsing. You can also go to the advanced options for untrusted sites and click a check box to forbid Web bugs.

To pick up any of these add-ons, see my . And for more, see the Mozilla site's huge selection of .