Mozilla is submitting its do-not-track capability as a draft specification to the IETF for review. The do-not-track (DNT) feature is built into the new Firefox 4 Web browser, which is currently at its first release candidate stage (RC1).

DNT is an effort to provide both Web users and advertisers with a mechanism to opt in or out of behavioral tracking and other online data collection.

Other browser vendors, including Google Chrome and Microsoft's IE, are also implementing their own versions of capabilities to prevent tracking. But in contrast to some of the techniques rival browsers are exploring, Mozilla is aiming to convey users' privacy intentions directly to ad networks and websites.

"What we did in Firefox 4 is we've put a preference in our product that tells websites when a user doesn't want to be tracked," Johnathan Nightingale, director of Firefox development at Mozilla, told InternetNews.com.

Nightingale explained that Firefox 4's DNT, when enabled, sends an HTTP header that says, DNT=1, which means: "do not track me."

"It's up to the ad networks whether they respect that or not, but this point it's a signal we never had before," Nightingale said. "We know it will evolve but we just wanted to start the conversation with a simple binary expression that I want to be tracked or I dont want to be tracked."

Currently Firefox 4 users aren't provided with a visual notification in the browser if a website supports Mozilla's DNT. Mike Beltzner, Mozilla's director of Firefox, told InternetNews.com that the hope is to be able to provide that as well as other information over time.

Users today can choose not to run JavaScript or to block cookies completely in an attempt to block tracking technologies. But with Firefox 4, Mozilla is not interested in blocking tracking cookies.

"That's the blacklist approach you get with Microsoft's IE9," Beltzner said. "The reason why we don't see that as a good mechanism is because a lot of site functionality relies on those cookies being there."

Beltzner added that simply blocking the cookie will lead to unpredictable results on the sites. He argued also that it would accelerate an arms race with advertisers as they try and get around the block.

"The thing I like least about the blocking option is that it doesn't express intent," Nightingale said. "So when you blacklist the browser just blocks the resource and the ad networks can legitimately claim that they didn't know that a user did not want to be tracked."

Nightingale stressed that Mozilla wants the ad networks and websites to know that users do or don't want to be tracked. Mozilla also doesn't want to get to the point where advertises move away from cookies to more intrusive mechanisms for collecting information.

"DNT allows the user to have a voice and it turns the onus around," Beltzner said. "So instead of the onus being on the user to block everything, the onus is on the website owner to respect what the user is asking for."

Sean Michael Kerner is a senior editor at InternetNews.com, the news service of Internet.com, the network for technology professionals.