• by Wendy Davis , Staff Writer @wendyndavis, March 17, 2011

When Mozilla said last year that it was going to include a do-not-track header in its Firefox browser, the central question raised by the feature was whether any online companies would honor it. After all, unlike systems that physically block tracking companies, a header can only communicates users' wishes to companies. Those companies themselves must then decide whether or not to honor those wishes.

It's still not clear how online companies overall will respond to the Firefox header. But in recent weeks, a group of more than 30 ad networks and behavioral targeting companies have come forward to say that they back Mozilla's approach and are urging all other companies in the space to respect the headers. "The FTC has recommended a simple header solution which is what Mozilla seems to be creating and what we believe industry should support," the groups say in a proposal that's being circulated to various self-regulatory groups, governmental officials and ad companies.

"I think that, while our first instincts might be to resist do not track, in many respects the ability for users to not be tracked has existed for a long time," says the initiative's architect, Dilip DaSilva, CEO of Exponential, which owns ad network Tribal Fusion. Other companies that have joined in the proposal include Burst Media and Audience Science. For instance, consumers can set their browsers to reject all third-party cookies.

In a previous version of the proposal, DaSilva and the other ad networks urged companies to interpret do-not-track headers as signaling that consumers wanted to eschew all forms of behavioral advertising, including first-party tracking by portal companies that own a variety of consumer-facing sites. But the groups recently backed away from that recommendation. "We started talking to the IAB and all the parties involved and realized that in certain areas we had gone too far," DaSilva says.

At the same time, DaSilva and the networks in the new coalition aren't endorsing all browser-based tools. They are particularly critical of Microsoft's IE9 tracking protection lists, which would prevent third parties from serving material on sites they don't own. The groups say that this feature could end up blocking content as well as ads. Microsoft additionally is turning on a do-not-track header for users who download any tracking protection lists, according to reports. DaSilva says he doesn't currently endorse that header because users themselves aren't activating it.

Regardless, the fact that some leading ad networks are now backing the Firefox do-not-track header appears to mark a major step forward for self-regulation. While the industry's official programs encourage cookie-based opt-outs, that mechanism poses some problems. Most obviously, opt-out cookies cookies aren't stable, given that somewhere around 30% of consumers are thought to regularly delete all third-party cookies, either manually or through software. But consumers aren't likely to turn off Firefox's do-not-track header by accident, the way they might unintentionally delete their opt-out cookies.