Mozilla has effectively postponed Firefox's controversial third-party cookie-blocking policy for several months.

Yesterday, the open-source developer announced it was collaborating with a new initiative, dubbed "Cookie Clearinghouse," or CCH, launched by Stanford University's Center for Internet and Society.

"Today Mozilla is committing to work ... to develop the CCH so that browsers can use its lists to manage exceptions to a visited-based third-party cookie block," wrote Brendan Eich, Mozilla's CTO, in a post on his personal blog.

The CCH, which is headed by Alexia McDonald, director of Stanford's Center for Internet and Society -- and formerly a part-time privacy research officer at Mozilla -- will come up with a list of sites to be blocked by browsers, as well as another that includes blocking exceptions.

Those lists would be analogous to the blacklists and whitelists used for other purposes, like those that prevent browser users from visiting potentially-malicious websites.

Such centralized, constantly-updated lists, said Eich, are necessary to solve the false positive and false negative results that have plagued Firefox's third-party cookie blocker.

Cookies are used by online advertisers to track users' Web movements, then deliver targeted ads. Firefox was to allow cookies presented from domains users actually visit -- dubbed a "first-party" site -- but block those generated by a third-party domain unless the user had previously visited the cookie's site-of-origin.

Examples of first-party cookies are those placed in a user's browser by sites like Amazon.com to identify the customer on repeat visits, letting him or her skip the log-on sequence. Third-party cookies, however, are often placed in ads on first-party sites so that advertisers and online ad networks can track a browser's past activity.

Earlier this year, the feature was set to debut in Firefox 22, which launches next Tuesday, June 25. Later, it seemed on track for Firefox 23, the edition slated to ship Aug. 6. But a month ago, Mozilla postponed cookie-blocking's implementation, saying it needed to "collect and analyze data on the effect of blocking some third-party cookies," specifically the impact of false-positives and false-negatives.

Months ago, when Mozilla's proposal appeared set to debut in Firefox 22, several online advertising groups, including the Interactive Advertising Bureau (IAB) and Association of National Advertisers (ANA), vehemently objected, claiming that the on-by-default blocking would "disenfranchise every single Internet user" and result in the shuttering of small businesses and small websites. An official with the ANA promised that Firefox users would see more ads, not fewer, if the feature was switched on.

Firefox's cookie blocking is essentially a clone of what Apple's Safari already does, and has done since its 2003 inception. Safari for iOS, the mobile operating system that powers the iPhone and iPad, has blocked third-party cookies since its 2007 debut.

But the decision to partner with McDonald's project means that third-party cookie blocking in Firefox, or other browsers, is much further in the future than August.

"We hope to complete Phase I in a few months, by Fall 2013," said the CHH website in a short FAQ published Wednesday. Phase I will involve decision-making on several fronts, including technical issues, such as the criteria for adding sites to the black- and whitelists, and the file format for those lists.

"Once the lists are in place, it will take time to populate them," the CCH FAQ continued. "Browsers choosing to use the lists will need time to test them before releasing them widely. While we will all work diligently and quickly, it is likely to take months before the entire system is live in a Web browser. [Emphasis not in original.] Browser plug-ins and add-ons may be available more quickly."

If the CCH's estimate is accurate, it will be months before Firefox actually fires up its cookie blocking in a production edition.

"We believe that the CCH will address some of the concerns we've identified with the third-party cookie-blocking patch that we are holding in Aurora," a Mozilla spokesman said. "The patch won't move to general release until we have had the opportunity to do our own instrumentation and to implement the design set out by the CCH. Given the moving pieces, we do not expect that to happen until sometime in Q4 at the earliest."

Firefox Aurora is the least-polished of the three main build channels Mozilla maintains. While features added to Aurora usually debut in the Release channel 12 weeks later, Mozilla will not shift cookie blocking to the Beta and then Release channels until it's satisfied with the white- and blacklists, and their integration with the browser.

This article, Mozilla again postpones Firefox third-party cookie-blocking, this time for months, was originally published at Computerworld.com.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is gkeizer@computerworld.com.

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