Mozilla engineers have borrowed yet another feature from the Tor Browser. Starting with version 58 Firefox will block attempts to fingerprint users using the HTML5 canvas element. Canvas fingerprinting works by loading a canvas HTML tag inside a hidden iframe and making the user’s browser draw a series of elements and texts. Mozilla engineers plan to prompt users with a site permission popup when a website wants to extract data from a < canvas > HTML element. This is similar to the permission shown when websites wish to access a user’s webcam or microphone.
Source: https://www.bleepingcomputer.com/news/software/firefox-implements-another-privacy-preserving-feature-taken-from-the-tor-browser/