Further: the Canvas API doesn’t have any requirements on rendering accuracy.

By deferring to the GPU, font library, etc, tracking code can generate an image that is in most cases unique to your machine.

So blocking the Canvas API would return a 0. Which is less unique than what it would be normally.

Iirc, Websites can’t query addons unless those addons manipulate the DOM in a way that exposes themselves.

They can query extensions.

Addons are things installed inside the browser. Like uBlock, HTTPS Everywhere, Firefox Containerr, etc.

Extensions are installed outside the browser. Such as Flashplayer, the Gnome extensions installer, etc.