8 essential privacy extensions for Firefox

Protect your online life from prying eyes with these key Firefox privacy add-ons.

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Cookies placed by ads and Web pages can be used to track you as you move from site to site: Every time you visit a page with code from a particular ad or other tracking network, it can check to see what other sites with its code you've visited, what you did there and what you clicked on, allowing it to build a rather thorough profile of your surfing habits.

If you prefer more private, less customized Web surfing, using your browser's security or privacy settings to block third-party cookies can help, but some tracking services are able to circumvent these controls.

Ghostery Firefox extension
Ghostery identifies the companies behind the tracking code on Web sites.

The Ghostery extension, a part of the Better Advertising project, identifies code from 200 different ad and other tracking networks, showing you who is collecting data about you and what data they are collecting. You can decide whether to allow each service to track you or to block it.

When a Web page is first loading, Ghostery overlays a list of active trackers at the top-right-hand corner of your browser. If you want to explore further, you can click the ghost icon in your browser's status bar to bring up a menu listing all the trackers along with links to further information.

Ghostery Firefox extension
Ghostery provides information about each tracking service so you can choose whether or not to let it track you.

You can even explore the particular code used to see exactly what the tracker is doing. Clicking "Block" for any tracker will prevent its JavaScript from loading at all, on the site you're currently visiting plus any other sites that use the same service.

Ghostery is also available for Internet Explorer and Chrome.


NettiCat's BetterPrivacy offers protection against an increasingly common kind of cookie called a local shared object (LSO) or Flash cookie. LSOs are used by the Adobe Flash Player plug-in to store the same kind of information that's usually stored in browser cookies.

However, because LSO cookies are stored in a system folder instead of in the browser folder, they can't be easily deleted. What's more, unlike browser cookies, LSOs never expire, and they can hold about 25 times more information than typical cookies.

Since these objects are placed by Flash, your browser's security settings have no effect on them. And here's where they get really insidious -- some companies use Flash cookies to duplicate their browser cookies. You may delete the browser cookie for a site, but the LSO stays -- and it restores the original cookie the next time you visit the site. This reanimation capability has given rise to two more names for these objects: super-cookies and zombie cookies.

This is where BetterPrivacy comes in. The extension can be set to automatically delete all Flash cookies every time you exit your browser, or you can manually manage and delete unwanted LSOs one by one so that information can't be accessed or used to track you from site to site.

When you install BetterPrivacy, there's no obvious change to Firefox off the bat. When you close the browser, however, the extension checks for LSOs. If it finds any, you'll see a dialog box asking if you want to delete them. If you hit Cancel, it doesn't do anything; if you hit OK, it deletes them. There's also a checkbox that lets BetterPrivacy automatically delete all LSOs every time after that.

BetterPrivacy Firefox extension
BetterPrivacy scans for and removes LSOs -- a.k.a. super-cookies -- every time you exit Firefox.

To manage LSOs directly, open BetterPrivacy's preferences in the Tools menu. Here you can remove them one by one or all at once; you can also add specific LSOs to a whitelist to prevent them from being automatically deleted in the future.

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