One of the many features included in the new Firefox 4 browser is support for the new HTTP "Do Not Track" (DNT) header. The browser broadcasts the header to all sites requesting that the server not install any tracking cookies on the machine. In what amounts to a solid endorsement of the standard, the Associated Press has decided to implement support for the DNT header.
This means that over 800 news sites will now abide by user preferences on the matter. It takes the DNT header from a good idea, to a viable system to protect user privacy. Mozilla is in talks with the Digital Advertising Alliance to get the group to voluntarily support the DNT header as well.
The DNT header is not technically a real standard as of yet. It still has to be adopted by the W3C before that can happen. Also, no one is forcing sites to recognize the header. Blocking cookies completely will still be the only way to know for sure.