It’s going to be an arm race and the most dedicated kids, not necessarily the smartest or wisest, will figure it out. Eventually they’ll get the concepts behind the tools they mindlessly use until then, eventually find much better tools allowing them to bypass a lot more restrictions.

Well.. it depends on how do you define "smart" ..but to me, that kind of dedication and resourcefulness is already showing problem-solving skills, regardless of whether they "get the concepts" (many adults don't fully understand the tools they use either).

I don’t see how a browser will be able to prevent this kind of usage

In Firefox, you can disable websockets (and most other features or about:config settings, but the website you linked uses websockets) through a policy.json setting writable only by root, so it wouldn't be possible for a user without root permissions to change it.