Browser Fingerprinting Test: Check Yours with Cover Your Tracks

Additional resource for the lesson “Your Browser’s Fingerprint with Cover Your Tracks” — Online Anonymity course

A browser fingerprinting test shows you what your browser tells every site you visit, without a single cookie: its language, time zone, screen, fonts and many other small details. Together they can make your browser stand out from the crowd. This resource walks you through the free Cover Your Tracks test, explains how to read the result calmly, and helps you decide what, if anything, to change.

A. Why this matters

In this course, privacy is deciding what others know about you; anonymity is being able to act without what you do being linked back to who you are. The question running through every resource here is linkability: what ties one visit to the next, and to you.

Cookies are the best-known link, and you can delete them. A fingerprint works differently. A site, or a tracking company working across many sites, reads the settings your browser already shares to display pages properly, and combines them. If that combination is rare enough, it can recognise your browser again next week, even after you have cleared everything.

That sounds worrying, but it is also something you can look at for yourself. A test like Cover Your Tracks turns an invisible mechanism into a page of results you can read, and your browser choice is one of the few places where a single decision changes a great deal.

What the sources say

The Electronic Frontier Foundation (EFF), a digital rights organisation, started this work in 2010 as a research project called Panopticlick, to investigate how unique each browser is. In 2020 it was rebranded and relaunched as Cover Your Tracks. The EFF defines browser fingerprinting as “a method of tracking web browsers by the configuration and settings information they make visible to websites”, and warns that it is “difficult to detect” and hard to thwart.

The UK’s Information Commissioner’s Office (ICO), the independent data protection authority, explains why fingerprinting is harder for people to control than cookies: it “relies on signals that you cannot easily wipe.” Even privacy-conscious users, the ICO notes, will find it difficult to stop. It also reminds organisations that data protection law, including the Privacy and Electronic Communications Regulations (PECR), applies, and that people should be given fair choices before they are tracked this way.

Mozilla, which makes Firefox, describes how the combination of browser details “can act like a ‘fingerprint’ and makes you identifiable across the web.” The Tor Project, which builds Tor Browser, points out the trap in trying to fix this alone: any extra option to choose how you appear “would only make users more unique and thus easier to fingerprint.”

B. Key concepts

Five ideas that help you run the test and understand what it tells you.

A fingerprint is a bundle of ordinary details

Browser fingerprinting means recognising a browser from the details it shares with every site: the browser and operating system version (the “user agent”), language, time zone, screen size, installed fonts, and how your device draws certain hidden images, known as canvas and WebGL. None of them identifies you on its own. The EFF calls them “seemingly insignificant data”.

Why it matters to you: Clearing cookies does not change any of these details. If you only ever think about cookies, you miss a link that may still be there.

Unique is not the same as identified

A test can tell you your browser looks unique among the browsers it has seen. That means a tracker could recognise it again from one visit to the next. It does not, by itself, mean anyone knows your name: that link usually comes from somewhere else, such as an account you sign in to.

Why it matters to you: Reading “unique” as “exposed” leads to panic changes. Reading it as “recognisable” helps you think about which other links, like being signed in, would complete the picture.

Bits: how much each detail narrows the crowd

Cover Your Tracks shows each detail with two figures: “Bits of identifying information” and “One in x browsers have this value”. The more bits, the fewer of the test’s recent visitors share that value: each extra bit halves the crowd. Why a handful of details adds up so quickly is explained in the re-identification resource in this section.

Why it matters to you: Bits let you see which detail does the most work. A rare set of fonts may say far more about your browser than its language does.

Blending in, or blurring the picture

There are two ways a browser can make your fingerprint less useful. One is to make many users look the same, so you hide in a crowd: this is Tor Browser’s approach, which reduces settings to a small set of standard options. The other is to randomise some values so they change between sites and sessions: Brave’s approach, in its own words a “best-effort defense”.

Why it matters to you: In a test, a blended browser looks common; a randomised one may look unique each time but cannot easily be linked from one visit to the next. Both are forms of protection, and they read differently in the results.

The paradox: more tweaks can mean more unique

The EFF warns that changing your settings and adding protections can make you easier to pick out: “An add-on intended to protect you can even lead to your full identification.” Every unusual extension, custom setting or rare font is one more detail that few others share.

Why it matters to you: The instinct to fix a fingerprint by adding tools often backfires. A mainstream browser with its built-in protection switched on usually does more than a long list of add-ons.

C. A practical example: Sara’s two browsers

Sara is 28 and teaches at a secondary school. She prepares lessons in the evening and uses the same laptop for school platforms, her own reading and the odd online order. A colleague mentioned fingerprinting in the staff room, and that evening she decided to run a browser fingerprinting test instead of worrying about it.

Her usual browser had collected a lot over the years: six extensions, including two privacy add-ons she had installed after reading an article, a handful of downloaded fonts for making worksheets, and a custom zoom level. The result surprised her: her browser looked unique among those the site had seen. Her system fonts, and the line showing that an ad blocker was in use, carried some of the highest bit counts on the list.

What changed when Sara looked again

Sara did the exercise in section D, without changing anything at first:

• In a second browser, freshly installed with standard settings and its built-in fingerprinting protection on, the answer to the fingerprinting question changed, and fewer details carried high bit counts.
• She noticed that the two privacy add-ons overlapped with what the second browser already did for her by default.
• She realised that her fonts were a work tool she was not going to give up, and that was fine.

She made two decisions. She removed one of the overlapping add-ons from her usual browser and switched on its built-in fingerprinting protection. And she started using the second browser for general reading, keeping the first for school platforms where she signs in anyway. She did not try to become invisible. She simply made her everyday reading harder to link to the rest of her browsing.

D. Try it yourself: a two-browser fingerprinting test (15 minutes)

Four short steps. You do not need to install anything new if you already have two browsers; if you have only one, step 3 can wait for another day. Whatever you find, it is a picture, not a grade.

Step 1 — Prepare a simple note (2 minutes)

• Open a note with two columns: “Usual browser” and “Second browser”.
• Under each, leave space for three lines: the summary, the three details with the most bits, and the number of extensions installed.
• Write down only what the test reports about your browser. You do not need to note any personal information.

Step 2 — Run the test in your usual browser (5 minutes)

• Open Cover Your Tracks (the EFF address is in section E) in the browser you use most, and start the test from the home page.
• Read the summary first: it answers whether your browser is blocking tracking ads and invisible trackers, and whether it is protecting you from fingerprinting.
• Then open the detailed view and look at the “Bits of identifying information” column. Note the three details with the highest numbers.

Step 3 — Run it again in a second browser (5 minutes)

• Use another browser on the same device, ideally one with built-in fingerprinting protection and few or no extensions. In Firefox, for example, Mozilla’s help page puts these options under Settings › Privacy & Security › Enhanced Tracking Protection, by choosing Custom.
• Run the same test and fill in the second column.
• Expect the figures to change if you re-run it later: the test compares you with people who have visited it recently, not with the whole web.

Step 4 — Compare and choose one change (3 minutes)

Look at the two columns side by side and pick one option:

• Keep it: your usual browser already shows protection, or the details that stand out are ones you need.
• Simplify it: remove one extension you no longer use or that duplicates a built-in feature, then re-test.
• Separate it: use the second browser for one kind of activity, such as general reading, so that it is not linked to the browser you sign in with.

One change you understand is worth more than ten settings copied from a forum.

Already covered in the Online Security course

Privacy Focused Browser: The Setting You Use All Day
It covers how to choose a privacy-focused browser for everyday use; this resource adds a way to check, with a fingerprinting test, how recognisable your current browser is and what a second one changes.

E. Videos, articles and further resources

The test itself first, then institutional guidance and the browser makers’ own documentation. All in English.

The test and how it works

Electronic Frontier Foundation — About Cover Your Tracks
What the test checks, how it measures uniqueness against recent visitors, what it logs, and the history of Panopticlick.
https://coveryourtracks.eff.org/about

Electronic Frontier Foundation — Learn (Cover Your Tracks)
A plain-language guide to trackers and fingerprinting, including why some protections can make you stand out.
https://coveryourtracks.eff.org/learn

Institutional guidance

Information Commissioner’s Office (UK) — Our response to Google’s policy change on fingerprinting
Why fingerprinting is harder to control than cookies, and the UK legal position.
https://ico.org.uk/about-the-ico/media-centre/news-and-blogs/2024/12/our-response-to-google-s-policy-change-on-fingerprinting/

Browser documentation

Mozilla Support — Firefox’s protection against fingerprinting
What Firefox blocks, the “Known fingerprinters” and “Suspected fingerprinters” options, and what to do if a site breaks.
https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting

The Tor Project — Fingerprinting protections
How Tor Browser keeps users blended together with a small set of standard options.
https://support.torproject.org/tor-browser/features/fingerprinting-protections/

Brave (GitHub wiki) — Fingerprinting Protections
How Brave blocks or randomises values that can be used to fingerprint a browser.
https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections

Links checked in November 2026. If an address changes, searching for the title on the organisation’s site usually finds it.

F. The Cyber Welfare Framework: Skills, Awareness, Secure Behaviour

This resource sits on the Skills pillar at level FL2 – Beginner: running a test yourself and reading what it says before changing anything.

Skills

• Running a browser fingerprinting test and reading its summary and detailed results.
• Spotting which details carry the most bits of identifying information.
• Finding the built-in fingerprinting protection in your own browser’s settings.

Awareness

• Understanding that a fingerprint is made of ordinary details, and that clearing cookies does not change it.
• Knowing that “unique” means recognisable, not identified by name.
• Recognising that extra add-ons and unusual settings can make a browser stand out more.

Secure Behaviour

• Preferring built-in protection in a mainstream privacy browser to a stack of extensions.
• Keeping extensions few, and removing the ones you no longer use.
• Separating activities across browsers when you want them not to be linked.

G. Questions to sit with

• Which of your browsing activities would you prefer not to be linked together, and which do you not mind?
• Which details in your fingerprint are there because you need them, and which just accumulated?
• How would you explain to a friend why “unique” in a test is information, not a reason to panic?

H. What to do now

The recommendations (R) and security measures (MS) from the Cyber Welfare database that apply most directly here.

1. Let the browser do the work

• MS5 — Use a privacy-respecting browser such as Firefox or Brave, and check that its built-in fingerprinting protection is switched on rather than relying on add-ons.
• If you consider Tor Browser for activities that need stronger anonymity, keep its standard settings: changing them is what makes you stand out. Rules on its use vary by country, so check where you live.

Minimum commitment: this week, run the test once in your usual browser and note the single detail with the most bits.

2. Keep your browser ordinary

• Review your extensions and remove any you no longer use, or that duplicate a protection your browser already offers.
• Avoid unusual tweaks copied from guides unless you understand what they change; re-test after any change you make.
• Use a separate browser for an activity you want kept apart, rather than trying to disguise a single browser.

Minimum commitment: remove one extension you have not used in the last month, then re-run the test and compare.

In short

• A browser fingerprinting test shows the bundle of ordinary details your browser shares, and how rare that bundle is.
• “Unique” means your browser could be recognised again, not that you are known by name.
• Built-in protection in a privacy browser usually helps more than extra add-ons, which can make you stand out.
• The goal is not invisibility: it is choosing which of your activities can be linked together.

Related resources in this course

• What Your IP Address Reveals: Location, Provider and Metadata
• How Websites Recognise You: Cookies, Ad IDs and Logins
• Re-identification: Why a Few Details Can Identify You

Discover more companion resources from the online courses of the Protect Your Digital Privacy programme.