Firefox's protection against fingerprinting

Like other browsers, Firefox’s functionality is influenced by your operating system, hardware, graphics cards, additional software, and even the fonts you install. Some website technologies, like HTML5 Canvas, can even uniquely identify you based on how your computer draws images.

Some websites, particularly those using HTML5 Canvas, look at this unique combination of factors and assign you a number, or a “fingerprint”, which makes you identifiable across the Web. This “fingerprint” is potentially used to profile you for targeted content without the use of cookies.

Currently, Fingerprinting Protection is an experimental feature that is under heavy development in Firefox. It is likely that it may degrade your web experience, so we recommend it only for those willing to test experimental features.

How am I protected?

If a website tries to extract your data, Firefox will warn you with a prompt in the address bar. You can choose whether to allow the website to extract your data. This is the most common way to observe this protection.

fingerprint prompt

However, the Canvas Permission Prompt is not the only thing that Fingerprinting Protection is doing. Fingerprinting Detection also looks at other factors:

  • Your timezone is reported to be UTC
  • Not all fonts installed on your computer are available to webpages
  • The browser window prefers to be set to a specific size
  • Your browser reports a specific, common version number
  • Your keyboard layout and language is disguised
  • Your webcam and microphone capabilities are disguised.
  • The Media Statistics Web API reports misleading information
  • Any Site-Specific Zoom settings are not applied
  • The WebSpeech, Gamepad, Sensors, and Performance Web APIs are disabled
This is not an exhaustive list - other features may be altered or disabled.

How do I enable or disable this protection?

Currently, Fingerprinting Protection is an experimental feature enabled by a confirmation flag set in about:config. It can also be enabled by Web Extensions.

Changing hidden settings can affect Firefox's stability and security. This is recommended for advanced users only.

  1. In the address bar, type about:config and press EnterReturn.

    • The about:config "This might void your warranty!" warning page may appear. Click I accept the risk! to continue to the about:config page.
  2. Search for “privacy.resistFingerprinting” and see if it is bolded and set to ‘true’. If so, you, or a Web Extension you installed, has enabled this preference. You can double click the line in about:config to toggle the setting.

If you discover the setting has become re-enabled, it is likely a Web Extension you have installed is setting it for you.

// These fine people helped write this article:Joni, tomrittervg, user1632815. You can help too - find out how.

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