The head of the advertising coalition at the forefront of the policy debate over new privacy protections for consumers blasted browser makers Microsoft and Mozilla at a Senate hearing Wednesday for derailing cross-industry work developing a feature allowing Internet users to opt out of behavioral tracking. But Lou Mastria, the managing director of the Digital Advertising Alliance, also found himself under fire during yesterday's hearing, with Senate Commerce Committee Chairman John Rockefeller (D-W.V.) accusing the advertisers that the DAA represents of "dragging their feet" in a technical working group developing technical standards for a "do-not-track" feature.In the meantime, Microsoft has activated do-not-track as a default in the latest version of Internet Explorer, while Mozilla has launched a limited trial program through which third-party cookies are automatically disabled in its Firefox browser.Skeptical of Internet AdvertisesFor Rockefeller, who made it clear that he is skeptical about whether Internet advertisers can be trusted to enact and abide by meaningful privacy regulations on their own, those efforts mark real progress of the kind that has been absent from the advertising camp.\n\n"We also know that legislating technology is risky. Given the current environment, though, it is clear that more is required, including continued congressional oversight."-- Harvey Anderson, Mozilla's general counsel.\n"Browsers are attempting to provide consumers with greater privacy protections, and ad networks are resisting these efforts. If you can say that I'm wrong, please prove it to me," Rockefeller challenged, pressing Mastria for answers about why a significant number of DAA members apparently continue to disregard Web headers indicating consumers' do-not-track preferences.[Related: Tech Groups Question New Do-Not-Track Bill]Mastria countered that the accord his association had reached with browser makers, regulators and other participants in the privacy debate had been undermined by the subsequent actions by Microsoft and Mozilla to incorporate additional privacy features into their browsers that had not been part of the original framework the parties had agreed to at a White House event last year."Unfortunately, the DAA agreement at the White House was short-circuited due to contrary approaches taken by both Microsoft and Mozilla," Mastria told the committee on Wednesday.It was after that accord was brokered, he noted, Microsoft went on to release a new version of Internet Explorer with do-not-track turned on as a default. "This is in direct conflict with the agreement they helped develop at the White house," Mastria charged.Then in February, Mozilla went a step further and announced the trial program that would block websites from serving third-party cookies through its Firefox browser.[Related: Obama Backs 'Consumer Bill of Rights' for Online Privacy]"These actions do not advance consumer choice, and they will have a significant adverse effect on users' Internet experience," Mastria said, warning that third-party cookies are not intrinsically a threat to user' privacy, but rather that they are a necessary mechanism to subsidize free content and services on the Web.Harvey Anderson, Mozilla's general counsel and senior vice president of business and legal affairs, emphasized that the blocking feature for third-party cookies is only in a preliminary "aurora" test, and that a larger but still limited beta test would be the next step. The product would also have some limitations if it rolled out for general availability, but for its capability to filter the large quantities of unseen tracking cookies regularly served up across the Web, it better comports with a reasonable understanding of privacy, according to Anderson."It creates a Web that reflects users' expectations," he said.[Related: FTC Issues Privacy Report, Calls for Do-Not-Track Tool]\n"Trust is the true currency that needs to be protected. The lack of trust stems from users not understanding the value proposition of online tracking. This is where industry can really make a difference -- if users don't understand what happens to their data, how it is used, or the tradeoffs, they will inevitably seek more protective blocking options," Anderson added. "We also know that legislating technology is risky. Given the current environment, though, it is clear that more is required, including continued congressional oversight."Who Can you Trust?\nSo the DAA accuses Microsoft and Mozilla of breaking the deal the parties reached at the White House, while Mozilla's Anderson said that the do-not-track signals users send through their browser "are largely ignored by the ad networks."\n\nThe legislative backdrop of Wednesday's hearing is a bill that Rockefeller introduced earlier this year that would establish mechanisms for implementing and responding to do-not-track, making that browser feature the law of the land. Rockefeller, who has announced that he will not seek reelection next year, introduced a similar bill in the last congress.More immediately, the World Wide Web Consortium (W3C), a standards body, has been convening a working group of stakeholders to develop technical specifications for do-not-track, next plans to meet in California in May.The W3C's work on the do-not-track standard has been slow, a delay the various parties -- notably the advertising representatives and browser makers whose views got an airing at Wednesday's hearing -- have explained with mutual accusations that their adversaries are negotiating in bad faith.Kenneth Corbin is a Washington, D.C.-based writer who covers government and regulatory issues for CIO.com. Follow everything from CIO.com on Twitter @CIOonline, Facebook, Google + and LinkedIn.