• by Wendy Davis  @wendyndavis, February 24, 2013

Mozilla's Firefox browser will soon block some third-party cookies by default, privacy advocate Jonathan Mayer announced on Friday on his blog.

The browser's upcoming version will include a patch, developed by Mayer, that blocks some third-party cookies -- like those set by ad networks. Mayer writes that the patch will be tested for 18 weeks.

Firefox's default settings will still allow first-party cookies, as well as cookies from third parties that users have a relationship with. "Only websites that you actually visit can use cookies to track you across the web," Mayer writes in a post explaining the patch.

Those settings are similar to the defaults in Safari, though Mayer characterized the Firefox cookie defaults as a "slightly relaxed version" of Safari's settings.

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.