Ad Networks Beware: Firefox to Block Third-Party Cookies

New policy could squeeze online behavioral advertising

The Interactive Advertising Bureau' lashed out Saturday at a new Firefox policy to block third-party cookies, effectively cutting off ad networks' ability to track users. That could be put a crimp in the growing online behavioral advertising business, but give privacy advocates a victory in their attempts to give users more control over their online information.

Mike Zaneis, the organization's svp and general counsel tweeted that Mozilla's new policy was nothing less than "a nuclear first strike against the ad industry."

Firefox will begin blocking the cookies from third-party ad networks by default beginning with distribution of Firefox version 22 on April 5. The browser would allow cookies from first party websites that users visit, according to Jonathan Mayer, a grad student at Standford University who wrote the patch for Mozilla.

Firefox's new cookie policy is similar to Apple Safari, but "slightly relaxed," Mayer said in a blog post

In practice, both Google Chrome and Microsoft Internet Explorer allow third-party cookies.

How much impact Firefox's new policy will have on online behavior advertising is hard to estimate; Firefox has about 20 to 30 percent of browswers. The big question is whether Microsoft and Google, the big two companies that depend on online advertising, will follow suit.

Microsoft last year raised the ire of the advertising community by rolling out a default Do Not Track browser header, which sends a signal to third parties not to track users. However, the ad community said it would not honor the setting.