Browser fingerprinting is used as an alternative to browser cookies by websites and web analytics services that want to distinguish users and track their online behavior.
Fingerprints use data that are collected passively from your web browser such as the version number, operating system, screen resolution, language, list of browser plugins and the list of fonts you have installed.
Acoording to Sophos:
“In canvas fingerprinting your browser is given instructions to render something (perhaps a combination of words and pictures) on a hidden canvas element. The resulting image is extracted from the canvas and passed through a hashing function, producing an ID,”
The new version of Firefox (version 58) will give the users the ability to block websites’ requests for data extracted via the HTML5 canvas element, which can be used to fingerprint their browsers.
There are many third-party plugins and add-ons (such as Canvas Defender) developed to help users recognize and block Canvas fingerprinting, Tor is the only browser that by default blocks Canvas fingerprinting. Mozilla decided to add this feature to its browser.
Now the browser will explicitly ask user confirmation if any website or service tries to use HTML5 Canvas Image Data in Firefox.