But I'm wondering if you are doing something wrong. I just tried nebula in Firefox 151.0.3 and it works flawlessly. Full screen works, all buttons in the player work. I also tried it on Firefox for Android and it works.
Do you have any other websites that don't work?
Even on a blank profile.
A lot of web devs simply do not test on anything else, even for billion and trillion dollar companies, I've seen it first hand.
This includes a lot of state and federal government websites.
Note: I have said nothing about nebula, I don't even know what that is if it's not the network overlay.
https://nebula.defined.net/docs/