• by Wendy Davis  @wendyndavis, August 10, 2021

Mozilla's Firefox browser is rolling out a new feature that it says will allow users to “delete all traces” of “sneaky third-party cookies” -- including so-called supercookies, which ad companies use to track web users who erase more traditional cookies.

“Today’s new version of Firefox Strict Mode lets you easily delete all cookies and supercookies that were stored on your computer by a website or by any trackers embedded in it,” the company said Tuesday when it unveiled the new “enhanced cookie clearing” function.

“When you decide to tell Firefox to forget about a website, Firefox will automatically throw away all cookies, supercookies and other data stored in that website’s 'cookie jar,'” Mozilla added. “This 'Enhanced Cookie Clearing' makes it easy to delete all traces of a website in your browser without the possibility of sneaky third-party cookies sticking around.”

For more than 15 years, ad-tech companies have attempted to use various types of supercookies to track people who delete traditional “HTTP” cookies. Doing so involves storing information about the websites that consumers visit in browser files that aren't erased when people shed their HTTP cookies.

In 2015, the internet standards group World Wide Web Consortium condemned supercookies, along with other forms of tracking that are difficult for users to control.

Firefox currently blocks some tracking cookies by default, but people who want the new beefed-up feature must opt in by enabling the “strict tracking protection” setting, which the company released in February.

Apple's Safari browser also blocks some tracking cookies by default, while Google's Chrome browser is expected to do so by 2023.