This add-on allows users to prevent websites from using some Javascript APIs to fingerprint them. Users can choose to block the APIs entirely on some or all websites (which may break some websites) or fake its fingerprinting-friendly readout API. If you encounter any problems please check the FAQ first. Please report issues and feature requests at https://github.com/kkapsner/CanvasBlocker/issues IMPORTANT: you should only have ONE addon/setting set that protects an API. Otherwise you could face massive performance issues. (E.g. EclipsedMoon for Palemoon has 'canvas.poison' which is known to cause issues: https://github.com/kkapsner/CanvasBlocker/issues/253#issuecomment-459499290) But setting privacy.resistFingerprinting to true and/or using the new fingerprinting protection introduced with Firefox 67 is fine. Protected "fingerprinting" APIs:

canvas 2d
webGL
audio
history
window (disabled by default)
DOMRect
navigator (disabled by default)
screen

More information on fingerprinting can be found at:

<canvas>: http://www.browserleaks.com/canvas
audio:
- https://audiofingerprint.openwpm.com/ (very poorly written = slow)
- https://webtransparency.cs.princeton.edu/webcensus/#audio-fp
DOMRect:
- http://jcarlosnorte.com/security/2016/03/06/advanced-tor-browser-fingerprinting.html
- https://browserleaks.com/rects

The different block modes are:

fake: Canvas Blocker's default setting, and my favorite! All websites not on the white list or black list can use the protected APIs. But values obtained by the APIs are altered so that a consistent fingerprinting is not possible
ask for permission: If a website is not listed on the white list or black list, the user will be asked if the website should be allowed to use the protected APIs each time they are called.
block everything: Ignore all lists and block the protected APIs on all websites.
allow only white list: Only websites in the white list are allowed to use the protected APIs.
block only black list: Block the protected APIs only for websites on the black list.
allow everything: Ignore all lists and allow the protected APIs on all websites.

Svar frå utviklaren