Webtransport Sample does not work on Firefox 122, Microsoft Edge 121, Opera GX

I've tested and tried it a few times. but it just doesnt work.
I've used https://googlechrome.github.io/samples/webtransport/client.html, and it doesnt want to connect.


If it helps, I tried it with a different Webtransport demo (https://webrtc.internaut.com/wc/wtSender12/), and got this errror:

This confuses me, because according to https://caniuse.com/mdn-api_webtransport, webtransport SHOULD be enabled on firefox

EDIT:
After checking my other browsers, it doesn't seem to work there either:
Opera GX:
Microsoft Edge

What's weird is that the internaut demo DOES work on both of them