The newest version of Mozilla’s Firefox browser includes a feature aimed at preventing companies from tracking people with “supercookies” — persistent identifiers that are harder for users to detect and delete than traditional cookies.

Firefox 85 includes “a fundamental change in the browser’s network architecture” that aims to defeat supercookies, Mozilla’s Steven Englehardt and Arthur Edelstein said this week in a blog post.

“We now partition network connections and caches by the website being visited,” they write. “Trackers can abuse caches to create supercookies and can use connection identifiers to track users. But by isolating caches and network connections to the website they were created on, we make them useless for cross-site tracking.”

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

For example, companies have placed tracking data in Flash storage and ETags. In 2013, KISSmetrics agreed to pay $500,000 to settle a class-action lawsuit settlement over claims that it stored data in ETags. Before that, Quantcast and Clearspring agreed to a $2.5 million settlement over claims that they stored data in Flash.

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.

“Tracking users’ activity without their consent or knowledge is … a blatant violation of the human right to privacy,” the organization’s Technical Architecture Group said at the time.