The maker of the popular Firefox browser is moving ahead with plans to block the most common forms of Internet tracking, allowing hundreds of millions of users to eventually limit who watches their movements across the Web, company officials said Wednesday.

Firefox’s developers made the decision despite intense resistance from advertising groups, which have argued that tracking is essential to delivering well-targeted, lucrative ads that pay for many popular Internet services.

Widespread release of the blocking technology remains months away. But officials at Mozilla, the nonprofit group that makes Firefox, spoke confidently Wednesday about the growing sophistication of tools they are building to limit the placement of “cookies” in users’ browsers.

These bits of code, often placed by data collection companies that users have never heard of, allow the companies to learn what sites a browser visits over months or even years. Firefox would still allow cookies if users were to give a Web site express permission, or if users were to visit a site regularly — as is common with shopping, social-media or news sites.

“We’re trying to change the dynamic so that trackers behave better,” said Brendan Eich, chief technology officer for Mozilla.

The Firefox browser is used by about 20 percent of the world’s desktop computers, according to NetMarketShare.

The blocking technology that Mozilla is developing borrows heavily from Apple’s Safari browser, which blocks all “third party” cookies, meaning tracking codes from sites that users do not intentionally visit.

Mozilla officials say they have refined that approach in recent months to allow third-party cookies in rare cases. For example, some sites use more than one Web address for security purposes and use cookies to make sure a user is recognized properly.

Mozilla also plans to add limits on cookies placed by sites that users intentionally visit, such as Facebook, to prevent tracking when users sign off and go to other sites. Mozilla plans to test and further refine its technology over the next few months before making it available to all users. No release date has been set.

“This is welcome news from Mozilla,” said Sen. John D. Rockefeller IV (D-W.Va.). “It proves there’s a market for giving consumers strong privacy protections . . . when online advertisers fall short.”

Randall Rothenberg, president of the Interactive Advertising Bureau, said the changes could disrupt Internet commerce, especially damaging smaller Web publishers that rely on the revenue brought by targeted advertising. He expressed hope that the industry could still persuade Mozilla to abandon or at least significantly alter its plans before widespread release. (The Washington Post Co. is a member of the Interactive Advertising Bureau.)

“There are billions and billions of dollars and tens of thousands of jobs at stake in this supply chain,” said Rothenberg, who called the browser makers “oligopolies” with excessive power to make decisions affecting the workings of the Internet. “It should be done with stakeholders’ input.

The technology under development at Mozilla also has been criticized by the Digital Advertising Alliance, an industry group. It has developed its own ad-blocking program that allows users to opt out of targeted ads by following links found on many Web sites.

The group says this program gives users choice while allowing those who want ads targeted to their interests to continue receiving them. “If you want to take that control, you can,” said Lou Mastria, managing director of the Digital Advertising Alliance. “We’re not sure why they need to upset the apple cart — an apple cart that consumers like.”

But privacy advocates say the alliance’s program is not easy for most people to find or use. Advocates have been urging Mozilla to push ahead with efforts to block tracking, which they have said could help distinguish Firefox from other browsers in a crowded industry.

The newest version of Microsoft’s Internet Explorer browser is preset to send a signal requesting that users not be tracked, but many advertisers are ignoring that request. Most browsers also have privacy settings that block all cookies, but users must activate these settings and they can make some Web sites malfunction.

What distinguishes the Firefox plan is that the browser would be preset to handle cookies in a way that blocks many types of tracking while allowing sites that users visit regularly to operate normally.

To help navigate the complexities of when to allow tracking, Mozilla has teamed up with Stanford University’s Center for Internet and Society to create a “Cookie Clearinghouse,” which will advise the company on how to tweak its settings to protect users. Makers of the Opera Web browser, popular on mobile devices, have also joined the Stanford-led initiative.

The clearest losers in Mozilla’s plan will be companies that track users without their knowledge. They will be permitted to request permission to place a cookie in Firefox, but users might have little incentive to allow a company they are not familiar with to have access their browsing data.

“For them, it is going to be difficult,” said Aleecia McDonald, director of privacy for the Center for Internet and Society. “Bringing them out into the light is not a bad thing.”

McDonald was formerly co-chair of a two-year-old effort to get the advertising industry, browser makers and privacy advocates to agree on an initiative called “Do Not Track,” which was endorsed by the White House and the Federal Trade Commission. It is aimed at giving users the ability to block tracking by changing the settings on their browsers, but the sprawling working group has struggled to reach a consensus.

Mozilla officials and McDonald said that if the “Do Not Track” effort yields an agreement, they might adjust Firefox’s blocking technology and the Cookie Clearinghouse to bring them in line with such a deal.

“This is a really good move for online consumers, no matter what happens with Do Not Track,” said Jeffrey Chester, executive director of the Center for Digital Democracy.

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