A visitor enters the Firefox pavilion at the Mobile World Congress in Barcelona, Spain, on Tuesday, Feb. 26, 2013. (Angel Navarrete/BLOOMBERG)

Mozilla, the non-profit group that makes the Firefox browser, says that it will delay its plans for rolling out a version of its browser that would increase restrictions on cookies — pieces of code that allow companies to monitor how people use the Web.

Developers said in March that a future version of Firefox could include a patch that automatically blocks cookies from sites that users have not visited directly, such as those placed by ad networks. Mozilla co-founder Brendan Eich gave an update on Firefox’s plans this week, saying on his personal blog that the non-profit organization wanted to do some more work on the feature before moving it to the next stage of testing.

Some advertisers have expressed concern about the effect blocking by default could have on their revenue. An official from the Interactive Advertising Bureau even called the patch a “nuclear first strike” against the ad industry, and consumer privacy advocates say that browser-makers may be under some pressure to back off the idea of cookie-blocking by default.

Addressing that issue, Eich stressed that Mozilla’s decision shouldn’t be seen as a reaction to those concerns.

“For those who read this as Mozilla softening our stance on protecting privacy and putting users first, in a word: no,” Eich wrote. “The patch as-is needs more work.”

The patch effectively mimics the settings already on Apple’s Safari browser. It also follows Microsoft’s decision to include cookie-blocking part of the “express” settings for its Internet Explorer browser. But Eich said it’s not working as precisely as Mozilla would like.

For example, he said, users may allow tracking for certain sites on one visit, but may change their minds on subsequent visits — particularly if the site in question changes the way it handles cookies. And in other cases, he said that the patch is blocking too much, cutting out trackers placed by sites that users have approved.

With those concerns in mind, he said, Firefox won’t turn the feature on by default for beta-testers, only for those using a version of the browser that’s earlier in the testing process.

He said Mozilla still plans to ship a version of the patch with the blocking on by default in the future, after testing.

Meanwhile, Mozilla’s Global Privacy and Public Policy lead, Alex Fowler, said that the organization is continuing talks with privacy advocates, the advertising industry and policymakers more broadly about how browsers should deal with cookies.

“We’ve undertaken a pretty extensive listening tour,” Fowler said in an interview with The Washington Post. “It’s not that we’re set on breaking cookies on the Web, it’s about moving users forward and creating a public conversation about privacy online.”

Advertisers, Fowler said, aren’t the only ones who have their issues with the patch. Mozilla has also heard concerns about the code from site operators in Europe, who said that the blocking was interfering with administrative tasks without providing any benefits to user privacy.

In tweaking how the function will ultimately work when Mozilla presents it to the regular consumer, Fowler said Mozilla is trying to figure out how make it a “scalpel, and not an ax.”

And while there’s a lot of debate over just how Mozilla decides to block its patch, Fowler said, he doesn’t think the conversation has to center on that point.

“We’ve been less focused on discussions of default settings, and been more outcome-focused,” Fowler said.

(The Washington Post Co. is a member of the Inter­active Advertising Bureau.)

Related stories:

Web browsers consider limiting how much they track users

Mozilla and third-party cookies

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