Firefox 85 only brought one significant user-facing change — add-ons are now directly installable from addons.mozilla.org. But it turns out there is a lot more going on under the hood. The latest version of the Mozilla browser is cracking down on supercookies that evade regular anti-tracking techniques.
To achieve that, Firefox now partitions network connections and caches by each individual website visited. In the past, Firefox would share some resources across websites to reduce overhead, a practice virtually all browsers engage in. But supercookies can abuse this system. Mozilla explains, “In the case of Firefox’s image cache, a tracker can create a supercookie by ‘encoding’ an identifier for the user in a cached image on one website, and then ‘retrieving’ that identifier on a different website by embedding the same image.” That’s a problem for all shared resources, which is why Firefox now loads the following caches for each website individually: HTTP cache, image cache, favicon cache, HSTS cache, OCSP cache, style sheet cache, font cache, DNS cache, HTTP Authentication cache, Alt-Svc cache, and TLS certificate cache.
Firefox 85 also partitions pooled connections, prefetch connections, pre-connect connections, speculative connections, and TLS session identifiers.
Mozilla promises that you won’t notice much of a difference when it comes to load time: “Our metrics show a very modest impact on page load time: between a 0.09% and 0.75% increase at the 80th percentile and below, and a maximum increase of 1.32% at the 85th percentile.” The company says that these are in line with impacts the Chrome team expects for similar planned changes to its caching practices.
Once you’ve updated to Firefox 85 on your desktop or Android, you’re automatically in on the changes regardless of which tracking protection level you choose. You can download the latest release from the Play Store or over at APK Mirror.