Worried about your Internet privacy? You should be, especially because of the latest Internet danger, so-called "evercookies." Evercookies store cookie data in multiple ways on a browser so that cookie tracking information can't be easily deleted. (Cookies, as you probably know, are bits of data on your hard disk that can be used to trace your Internet habits, although they can also be used to remember your login information at Web sites.) The usual tools for getting rid of cookies won't work on evercookies. But there's a tool that claims to kill them, while still letting you keep useful cookies on your hard disk: free Firefox add-in Anonymizer Nevercookie. Run Nevercookie, and its creators say you'll be safe from the intrusive evercookie technology.
It can be confusing to use Anonymizer Nevercookie at first. Install it, and then launch Firefox. When you launch Firefox after you've installed Nevercookie, a Choose User Profile screen may appear if you haven't used Firefox profiles previously. That screen appears because when you use Nevercookie with Private Browsing, a temporary profile is set up for each browsing session as a way to protect your privacy. If you don't want to see the screen appear every time, select the "default" profile, check the box next to "Don't ask at startup," and then click Start Firefox.
When Firefox starts, you won't yet be protected. You need to use Firefox's Private Browsing mode by choosing Tools -->Private Browsing, or else pressing Ctrl-Shift-P. A Private Browsing screen appears, and then a box appears telling you about using Nevercookie. Click OK. A second Private Browsing screen appears, with the toolbar colored blue. When you use that private browsing screen, Nevercookie will be protecting you. (It won't protect you if you use the non-blue, original Private Browsing screen.) Note that in this blue Private Browsing screen, the Nevercookie add-on won't show up if you select Tools-->Add-Ons. But it's there, keeping you safe.
Anonymizer Nevercookie is more a proof-of-concept than anything else at this point, because it doesn't integrate into your normal browsing sessions, and works only in Private Browsing. Still, if you're worried about evercookies, and are willing to browse the Web in Private Browsing mode, you'll find it useful.