# Mozilla: Firefox 143 fingerprint protections cut uniquely identifiable users from 75% to 46%

- Published: 2026-11-10 22:57 UTC
- Section: Digital & Computing › Data security
- Tags: browser fingerprinting, Firefox 143, Mozilla study, unique users 75% to 46%, Fingerprint Pro, Signifyd, Simpson Index, Shannon entropy, OHTTP, web compatibility
- URL: https://realtech.media/news/rt-a68995063de02059ea194657_mozilla_firefox_143/

**Mozilla measured fingerprintability on almost 25 million Firefox release users and built protections on the data; web compatibility was kept.**

![Mozilla: Firefox 143 fingerprint protections cut uniquely identifiable users from 75% to 46%](https://ecosistemastartup.com/wp-content/uploads/2026/11/firefox-143-privacidad-web-1200x675.jpg)
*ecosistemastartup.com*

Mozilla researchers, together with colleagues from the University of Toronto and UC San Diego, published a study of browser fingerprinting based on telemetry from almost 25 million Firefox release users, according to the companion site fingerprinting.study [1]. The protections designed from these data shipped in Firefox 143. The authors report that they reduced the share of uniquely identifiable users from 75% to 46% while maintaining web compatibility [1]. The measurements used privacy-preserving technologies such as OHTTP, so no individual user could be identified or tracked across the web [1].

## What makes a browser unique

The authors report that fingerprintability is driven largely by a small set of high-impact characteristics and their combinations, not by the accumulation of many independent measurements [1]. For Fingerprint Pro, the most discerning fingerprinter in the model, 80% of the users it sees as unique are already unique after 8 metrics, although it collects over 50 [1]. Signifyd collects over 80 metrics but identifies fewer users as unique: 80% of those it sees as unique are identified after 9 metrics [1].

The authors advise caution with any single percentage for "how many users are unique", because it merges populations that behave differently [1]. The operating system is always exposed to a fingerprinter: spoofing it breaks shortcut keys and gives wrong downloads, among other problems [1]. The team therefore segmented the population by operating system. Each system has different important metrics, and every aggregate figure has a per-OS breakdown [1].

## Beyond Shannon entropy

Shannon entropy is the standard yardstick in this literature, but the study shows that a high value does not reliably predict fingerprinting impact [1]. Earlier analyses counted unique users and did not examine everyone else. Those users could be 1 million people sharing one fingerprint or 500,000 distinct fingerprints shared by 2 people each [1].

To capture that difference, the authors use the Simpson Index, also known as the Herfindahl–Hirschman Index, to compare sets of cohorts, meaning groups sharing a fingerprint. This lets them compare defenses not only by how much uniqueness they eliminate [1].

The site also publishes the paper, appendix data, privacy-preserving aggregate data and analysis code, a description of data collection, an interactive test that compares a user's browser with the measured population, and a discussion board for proposing follow-up research [1].

## Sources

1. [fingerprinting.study](https://fingerprinting.study)
2. [ecosistemastartup.com](https://ecosistemastartup.com/firefox-143-reduce-la-huella-digital-del-75-al-46)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-a68995063de02059ea194657_mozilla_firefox_143/