Mozilla has detailed new Firefox defenses designed to make browser fingerprinting less precise, following a large-scale study of the signals that tracking systems use to distinguish one device from another. The company says the research drew on measurements from nearly 25 million Firefox users and informed protections whose latest components shipped in Firefox 145.
Browser fingerprinting does not require a conventional tracking cookie. A script can combine ordinary details such as available fonts, screen dimensions, graphics behavior and processor information into a profile that may be distinctive enough to recognize a browser across sites. Mozilla's research examined which combinations contributed most to uniqueness, with the goal of concentrating defenses on a relatively small number of high-value signals.
The resulting changes reduce unnecessary differences in what Firefox reports to websites. Mozilla gives screen information as one example: the browser can conceal details that would reveal the size or position of a desktop taskbar or dock. It can also group processor counts into values such as four or eight rather than exposing the exact number. Other work produced more consistent image rendering, Web Audio behavior and mathematical operations on Android. Firefox also randomizes some signals, although Mozilla says those measures were outside this study's evaluation.
Mozilla reported that the combined protections reduced the share of users with unique fingerprints and increased the number of users who appeared in the same groups. The company did not claim that fingerprinting had been eliminated. Tracking providers can change their methods, and privacy measures must be balanced against information that websites legitimately need, including language and time-zone settings.
The study used simulated measurements associated with scripts from Fingerprint Pro, Signifyd and Akamai. Mozilla said it added privacy safeguards to the telemetry collection, including Oblivious HTTP. Under that arrangement, a relay sees an IP address without seeing the encrypted request contents, while Mozilla receives the contents without the originating address. Individual telemetry records were later deleted and only aggregate results retained for publication. The research paper was accepted for the 2026 ACM Conference on Computer and Communications Security.
Some measures, including hiding taskbar or dock dimensions, are enabled in all browsing modes. Other defenses first appear in Private Browsing or Firefox's Strict Enhanced Tracking Protection mode while Mozilla evaluates compatibility before considering broader defaults. Users can select Strict mode for the additional protections, though Mozilla warns that stronger restrictions can interfere with some sites. The work complements Total Cookie Protection, which isolates cookie-based identifiers, but targets a different class of tracking that can operate without stored state.
