Mozilla's Firefox browser will soon block some third-party cookies by default, privacy advocate Jonathan Mayer announced on Friday.
Those settings are similar to the defaults in Safari, although Mayer characterized the Firefox cookie defaults as a "slightly relaxed version" of Safari's settings. Firefox currently commands around 20% of the desktop browser market -- four times as much as Safari.
Online ad companies will almost certainly try to rally opposition to the move. Mike Zaneis, general counsel at the Interactive Advertising Bureau, tweeted on Saturday that the setting "would be a nuclear first strike" against the ad industry.
The move comes around 18 months after the World Wide Web Consortium -- a group of computer scientists, industry representatives and privacy advocates (including Mayer) -- began trying to develop standards for responding to do-not-track headers. Those headers, now offered by all the major browsers, are aimed at letting people permanently opt out of online behavioral advertising. But the headers don't actually prevent tracking. Instead, they send signals to publishers and ad networks, which those companies decide how to interpret.
So far, the W3C hasn't been able to agree on how to interpret the signals. Some privacy advocates previously warned that if W3C fails to reach a consensus, browser manufacturers might follow Safari's lead and simply block third-party cookies.