It's kind of ironic how this doesn't work in Firefox.

On what platform? Works here.

    macOS Tahoe 26.5.2 (25F84)
    Firefox 152.0.5 (aarch64)
EDIT: Updated, still works on Firefox 152.0.6 (aarch64)

It worked for me but I had to enable something in about:config

javascript.options.wasm_js_promise_integration

Worked in my Firefox on Steam Deck. I was amazed it could run YouTube.

So funny story, supporting web codecs may have been a bad idea because it led to people using more traffic per session than we assumed at first. We had to add more servers mid HN post

We had completely saturated NICs on like the two original servers