Which browser features (fingerprinting protections, extensions, user agent) most reduce fingerprint entropy?
Executive summary
Browsers that enforce strong anti‑fingerprinting measures—like Tor Browser’s identical fingerprinting and Firefox 145’s “Phase 2” protections—produce the largest reductions in fingerprint uniqueness, with Mozilla reporting a drop from 65% trackable to 35% after Phase 1, and to about 20% after Phase 2 in lab measures [1] [2]. Extensions and user changes (adblockers, JS disabling, VPNs) help but are less effective and can stand out or break sites; Tor and purpose‑built anti‑fingerprinting defaults remain the single biggest entropy reducers [3] [4].
1. Big wins come from browser‑level defaults, not add‑ons
The clearest single lever to reduce fingerprint entropy is a browser that applies broad protections by default: Tor Browser’s design causes users to present “identical” fingerprints, creating a large anonymity set, and Mozilla reports its Firefox Phase 1 protections cut the fraction of uniquely trackable users from ~65% to ~35%, with Phase 2 further reducing that to ~20% in their analysis [3] [1] [2]. These changes work because they standardize or spoof multiple high‑entropy signals (canvas, fonts, cores, WebGPU, etc.) across users rather than trying to block individual scripts.
2. Which features reduce the most entropy — a practical ranking
Based on the coverage in the sources, the largest single contributors to entropy reduction are: whole‑browser anti‑fingerprinting that standardizes answers across users (Tor, Firefox protections) [3] [2]; blocking or spoofing high‑variance APIs like canvas, WebGPU, audio context and hardware concurrency, which Firefox and Tor explicitly target [3] [1]; extensions/adblockers that block known third‑party fingerprinting scripts — helpful but incomplete and dependent on lists [4]; and user tweaks (changing user‑agent, disabling JavaScript, using VPNs) which can reduce some signals but often break sites and may make you stand out [5] [6]. Sources emphasize browser‑level hardening as the most reliable entropy reducer [3] [2].
3. Extensions and user agents: helpful, but risky and partial
Adblockers and script blockers (uBlock Origin, etc.) can stop many fingerprinting scripts, and some browsers expose indicators when protected APIs are invoked, but these tools only reduce the footprint of known, detectable scripts and do not stop passive signals like installed fonts or GPU quirks [4] [5]. Changing your User‑Agent string or running unusual extensions can reduce some signals, but sources warn you may become unique precisely because the change is uncommon — making you easier, not harder, to re‑identify [4] [5].
4. Tradeoffs: usability, compatibility and conspicuousness
All sources note tradeoffs. Strong protections that randomize or standardize data can break legitimate site functionality (Firefox warns users can disable protections site‑by‑site) and extremely strict modes can make a user cohort small enough to be conspicuous (Brave sunset its “Strict” mode partly over that concern) [1] [7]. Disabling JavaScript or blocking APIs reduces data leakage but often renders many sites unusable; changing many signals manually risks standing out as an outlier [1] [4] [7].
5. What the browser makers themselves are doing and why it matters
Mozilla frames its changes as systemic: Phase 1 reduced trackability from 65% to 35%, and Phase 2 adds spoofing/limiting of data (e.g., reporting two processor cores) to push unique fingerprinting nearer to 20% — a measurable, cross‑vector reduction that no extension can replicate alone [1] [2]. Tor and privacy‑focused projects explicitly aim for homogeneity; Brave focuses on making standard protections robust while avoiding web‑breakage caused by overly small, strict cohorts [3] [7].
6. Missing or disputed details and limitations in the record
Available sources do not provide a unified, quantitative “bits of entropy saved” measure per feature; Mozilla gives percentage reductions in trackability but independent, comparable entropy metrics across browsers and configurations are not in the linked reporting [1] [2]. Claims that extensions or VPNs fully prevent fingerprinting are contradicted by multiple sources that describe fingerprinting as pervasive and able to use many passive signals beyond network addresses or scripts [8] [4].
7. Practical guidance: what actually lowers entropy for real users
If your goal is the biggest, measurable drop in fingerprint uniqueness, use a browser that standardizes fingerprints by default (Tor Browser or Firefox’s tightened private/strict modes) rather than piecing protections together with extensions [3] [2]. Complement with reputable script‑blocking or tracker‑blocking extensions if needed, but expect diminishing returns and potential site breakage. For high‑risk needs, prefer Tor or browser profiles designed to sit in large anonymity sets rather than bespoke fingerprints that may isolate you [3] [1].
Sources referenced: Combined reporting on browser anti‑fingerprinting measures, including Tor and Firefox testing and vendor blogs [3] [1] [2] [4] [7] [5].