Mozilla is making Firefox the first browser which will give users the option to disable canvas fingerprinting. This is a technique that is used by ad networks to track specific users around the web. It does not rely on cookies but is a twist on the universally supported HTML5 canvas elements.
Canvas fingerprinting works by making the browser render a hidden line of text or a 3D graphic using the HTML5 canvas element. This action generates a unique token because it's based on a lot of variables, including the system's GPU, operating system, browser, drivers, and installed fonts. This enables ad networks to track users without leaving a trace on their PC.
ExtremeTech reports Firefox will prevent canvas fingerprinting by returning a blank image unless the user gives consent:
The Tor Browser, which is based on Firefox, is designed to preserve user privacy. Naturally, it blocks the use of canvas fingerprinting. The browser simply returns a blank image until the user has granted the canvas access permission. Now, that restriction is feeding back into Firefox to protect users of that browser from surreptitious snooping by advertisers. This is part of the Tor Uplift Project to bring features from Tor into Firefox, whereas it has previously always been the other way around.
Ad tracking based on canvas fingerprinting has been widely used since 2014. Firefox 58 will be the first mainstream browser with technology to prevent canvas fingerprinting. Mozilla plans to release this version on January 16, 2018.