The U.S. Federal Trade Commission requested a mechanism to block online tracking, Mozilla offered Do Not Track technology to prevent Web pages from tracking people’s online behavior for advertising purposes. That means sites you’ve visited can leave cookies on your computer but ad networks that don’t already have one on your machine can’t.
Some people think it’s a matter of privacy. What if, for instance, you’re researching something online that you don’t want anyone to know about or associate with you. Things like a medical condition, political issue or religion? Firefox 22 will release April 5. Apple’s Safari and Firefox do not allow third-party cookies, Google’s Chrome and Microsoft’s Internet Explorer still allow them by default.