• by Wendy Davis  @wendyndavis, April 8, 2013

Despite pressure from ad industry groups, Mozilla is moving forward with its controversial plan to block third-party cookies by default in Firefox 22.

The company has just added the cookie-blocking patch to the “Aurora” version of the browser, according to Stanford grad student Jonathan Mayer, who developed the patch. Mayer noted the move on Twitter late last week. After testing the feature in Aurora, Mozilla will migrate it to the Beta version, and then will release it in the next version of Firefox -- currently slated for release this June.

Privacy advocates support Mozilla's plan, but the Interactive Advertising Bureau and Association of National Advertisers have come out strongly against the move. The ANA calls Mozilla's decision "extraordinarily counterproductive for consumers and business,” while IAB general counsel Mike Zaneis characterized it as a "nuclear first strike" against the ad industry.

All of the major browser manufacturers offer do-not-track headers that consumers can activate, but ad networks and publishers don't have to comply with them. By contrast, Firefox's new setting would actually block ad networks, exchanges and other third parties from setting tracking cookies, which are used to track users' behavior across the Web and serve them ads based on their presumed interests.

Although Apple's Safari has blocked third-party cookies for years, that browser's market share is only around 5%. But Firefox's market share is around 20%, which is large enough that the ad industry is concerned.

Not all participants in the online ecosystem oppose Mozilla's move. The Online Publishers Association -- primarily made up of large and medium-sized publishers -- says that Mozilla's new default settings could help spark an agreement about how to balance consumers' privacy with business needs.

“We're not endorsing what Mozilla's doing,” OPA President Pam Horan tells Online Media Daily. “But it's an opportunity for the industry to establish an ecosystem-wide solution.”

Mozilla's move comes as the World Wide Web Consortium's efforts to come up with a privacy standard have stalled. The W3C's Tracking Protection Group -- made up of advocates, industry representatives and computer scientists -- has been trying for around two years to reach an agreement about how to interpret browser-based do-not-track headers.

But the advocates and industry haven't been able to agree on what type of data companies can collect when people say they don't want to be tracked. Privacy advocates say companies should stop collecting information from users who activate do-not-track, but ad companies have said they want to continue to collect analytics information from users.