It's broken in Chrome too - there's no content asides from 'Reach three fibre' and the links. I would have expected at least a description to exist on the page.
It's a work-in-progress demo of react-three-fiber. There's a good explanation of what it is on the Github page - https://github.com/drcmda/react-three-fiber
Firefox 65.0.1 (64bit), Linux (5.0.0).
There are a couple warnings about a particular extension:
> warning: extension `GL_ARB_gpu_shader5' unsupported in fragment shader
The rest just appears to be successful parsing messages.
(But it worked really well in Konqueror & Chromium, so that's something.)
Safari and Chrome both had to work around the same thing, so it seems like there's some contention around who is to blame here.
Either way, three.js is (partially) broken for Firefox users.