Mozilla’s Firefox web browser could block tracking cookies by default.

A new privacy feature for Mozilla’s Firefox web browser could make life harder for online marketers, according to the Interactive Advertising Bureau, a trade group.

Mozilla, the nonprofit organization that maintains the Firefox browser, says it is testing a feature that would prevent web sites from automatically installing tracking cookies from outside companies.  Those cookies are bits of software that ad networks and other marketing and analytics companies install in consumers’ web browsers when shoppers visit sites in order to track their activity and store preferences, such as user names and preferred language. The trade group says deploying the feature that Mozilla is testing would harm small retailers.

“If third-party cookies are blocked, thousands of ad-supported small businesses—start-ups, small publishers, and mom-and-pop shops—will be forced to close down,” says Randall Rothenberg, president and CEO of the IAB. “These small businesses can’t afford to hire large advertising sales teams. Advertisers can’t afford the time to make individual buys across thousands of web sites.”

According to web analytics provider StatCounter, which measures more than 15 million page views per month across more than 3 million web sites, Firefox is the third most popular web browser worldwide. In February 2013, 21.34% of global page views were through Firefox, compared with 29.82% through Microsoft’s Internet Explorer and 37.09% through Google Inc.’s Chrome browser, it says.

Mozilla on Feb. 25 announced on its privacy blog that it had begun testing the changes. Were the changes to go live, consumers could still allow tracking by adjusting their privacy settings manually.

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To demonstrate how the changes would impact a typical web browsing session, Mozilla showed in the blog that, during a sample visit to four weather and news web sites, Firefox blocked more than 300 third-party cookies, allowing just 75 first-party cookies—those coming from the web sites directly—to install.

High-end furniture seller Carolina Rustica, which says it earns most of its sales online, could take a small revenue hit if Mozilla follows through with the changes, says president Richard Sexton, though he isn’t certain by how much. About 30% of the retailer’s marketing budget goes toward presenting consumers who have visited the retailer’s site with retargeted advertising on other web sites, and about 15% of those visitors use Firefox, he says. (Mattress USA Inc., No. 383 in the Internet Retailer Top 500 Guide, bought Carolina Rustica in October.)

The Firefox privacy changes will not immediately roll out to all Firefox users, says Brendan Eich, chief technology officer at Mozilla. Rather, the changes are still going through what Mozilla expects will be months of technical and user evaluations before an official trial group could test them, he says.  

Eich says that Firefox is not the first web browser to consider enabling a stricter cookie policy by default. Apple Inc.’s Safari web browser, for one, already automatically blocks all third-party cookies. The IAB isn’t concerned about Safari because of its consistently small share of global browser usage—according to StatCounter, just 8.6% of global page views were through Safari in February—versus that of Firefox, which facilitates about a fifth of global page views, it says. In more than a decade of Safari operating that way, no small businesses have been harmed, says David Jacobs, an analyst at the Electronic Privacy Information Center, a non-profit research center. He adds that e-retailers in general base only a small fraction of their advertising on behavioral data from third-party cookies.

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