The feature is based on "Client-Side Storage Partitioning," a new standard currently being developed by the World Wide Web Consortium's Privacy Community Group.
"Network Partitioning is highly technical, but to simplify it somewhat; your browser has many ways it can save data from websites, not just via cookies," privacy researcher Zach Edwards told ZDNet in an interview this week.
"These other storage mechanisms include the HTTP cache, image cache, favicon cache, font cache, CORS-preflight cache, and a variety of other caches and storage mechanisms that can be used to track people across websites."
Edwards says all these data storage systems are shared among websites.
The difference is that Network Partitioning will allow Firefox to save resources like the cache, favicons, CSS files, images, and more, on a per-website basis, rather than together, in the same pool.
This makes it harder for websites and third-parties like ad and web analytics companies to track users since they can't probe for the presence of other sites' data in this shared pool.
According to Mozilla, the following network resources will be partitioned starting with Firefox 85:
Intermediate CA cache
TLS client certificates
TLS session identifiers
But while Mozilla will be deploying the broadest user data "partitioning system" to date, the Firefox creator isn't the first.
Edwards said the first browser maker to do so was Apple, in 2013, when it began partitioning the HTTP cache, and then followed through by partitioning even more user data storage systems years later, as part of its Tracking Prevention feature.
The Mozilla team expects similar performance issues for sites loaded in Firefox, but it's willing to take the hit just to improve the privacy of its users.
"Most policy makers and digital strategists are focused on the death of the 3rd party cookie, but there are a wide variety of other fingerprinting techniques and user tracking strategies that need to be broken by browsers," Edwards also ZDNet, lauding Mozilla's move.
PS: Mozilla also said that a side-effect of deploying Network Partitioning is that Firefox 85 will finally be able to block "supercookies" better, a type of browser cookie file that abuses various shared storage mediums to persist in browsers and allow advertisers to track user movements across the web.