One of the new features that Mozilla introduced in Firefox 4 is a Do Not Track (DNT) setting. When the user enables the DNT option in the browser's preference dialog, Firefox will transmit a custom header in HTTP requests that will inform servers that the user wants to opt out of Internet tracking. The concept has obvious merit because it provides a simpler, more predictable, and more consistent approach than the cookie-based mechanisms that are currently used today to signify opt-out status.

The downside of Mozilla's system is that it would be completely ineffective without buy-in from the major advertisers. Despite the fact that it wouldn't actually do very much, Mozilla offered the setting in Firefox 4 with the hope that it would help build momentum for the superior opt-out mechanism. Its decision to do so seems to have been vindicated. In an announcement, Mozilla revealed that the DNT header is starting to gain high-profile supporters

Mozilla says that the AP News Registry has implemented support for the DNT header across 800 news sites with 175 million unique visitors. Users who visit those sites in Firefox and have the browser's DNT option selected won't be tracked. This is a nice step in the right direction for DNT adoption.

Mozilla says that it is also in talks with the Digital Advertising Alliance (DAA), which is exploring the possibility of incorporating DNT header support in its internal self-regulatory program. The DAA represents over 5,000 companies in various segments of Internet media and marketing. Uptake by the DAA would further legitimize Mozilla's DNT header and could potentially encourage other browser vendors and advertising consortia to follow.

As we have pointed out in some of our previous coverage of DNT technologies, the Internet advertising industry has a long history of voluntary compliance on tracking opt-out and a relatively decent track record of cooperation with privacy advocates. The industry already supports its own set of somewhat fragmented cookie-based solutions, but will likely be happy to converge around the DNT header proposal.

Although it looks like the DNT header is on a trajectory to become a de facto standard, it's important to understand that the feature is simply broadcasting an opt-out preference to servers and isn't actively blocking tracking. Users who want optimal protection from tracking will still have to find a more proactive blocking solution.