Third-Party Blocking Moves Forward For Mozilla's Firefox Browser
June 21, 2013

Third-Party Blocking Moves Forward For Mozilla’s Firefox Browser

Enid Burns for – Your Universe Online

After a period of review, Firefox decided to go ahead with plans to block third-party cookies for its new version of the web browser. The non-profit organization, Mozilla, will work with Aleecia McDonald of the Center for Internet and Society and the Cookie Clearinghouse (CCH) to manage blocked and allowed cookies.

Mozilla plans to block third-party cookies to eliminate false positives and false negatives. Mozilla co-founder and chief technical officer Brendan Eich explained the logic of the company's decision on his blog:

-- We want a third-party cookie policy that better protects privacy and encourages transparency.

-- Naïve visited-based blocking results in significant false negatives and false positive errors.

-- We need an exception management mechanism to refine the visited-based blocking verdicts.

-- This exception mechanism cannot rely solely on the user in the loop, managing exceptions by hand. (When Safari users run into a false positive, they are advised to disable the block, and apparently many do so, permanently.)

-- The only credible alternative is a centralized block-list (to cure false negatives) and allow-list (for false positives) service.

"I'm very pleased that Aleecia McDonald of the Center for Internet and Society at Stanford has launched just such a list-based exception mechanism, the Cookie Clearinghouse (CCH)," Eich said in his blog post. "Today Mozilla is committing to work with Aleecia and the CCH Advisory Board, whose members include Opera Software, to develop the CCH so that browsers can use its lists to manage exceptions to a visited-based third-party block."

Mozilla seeks feedback for the proposed methods the CCH will deploy on the Firefox Aurora patch, which is still in development.

Firefox Aurora will make use of the CCH list to allow or deny third-party cookies. Apple's Safari browser already blocks third-party cookies.

The advertising industry has hotly disputed Mozilla's decision, with support from the industry group the Interactive Advertising Bureau. Many sites use third-party cookies to identify site visitors in an anonymous manner. The cookies are set by ad networks and analytics platforms, and track certain behavior on a particular website, or across a network.

"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," reports Washington Post.

"Mozilla's decision to block third-party cookies is a line in the sand for the advertising industry. We're trying to change the dynamic so that trackers behave better," The Washington Post cites Eich as saying.

Firefox is the second most popular browser. According to, Firefox comprises 27.7 percent of the browsers on the internet, following Google's Chrome browser at 52.9 percent.

The tactics to be employed by Mozilla are a response to the failure of the Do Not Track standards.

One criticism of the Do Not Track practice is that it still leaves a cookie in a user's browser so web sites know not to track the user. When the cookie is deleted, the site has to place a new cookie in the browser.