So this is interesting.

I am running this on a Mac (Intel), on clean install of Firefox.

It didn't work.

If anyone is curious I'll post what I think might be relevant.

I got this error:

Uncaught (in promise) TypeError: can't access property "getPreferredCanvasFormat", navigator.gpu is undefined
    main https://auberon.xyz/deathray/:15

But I looked at the documentation for getPreferredCanvasFormat() and it exist.

mdn_: GPU: getPreferredCanvasFormat() method

So I looked at about:config and I listed what I think might be relevant: