Fix embedded Youtube video's "Sign in to confirm you are not a bot" problem if you are already signed in

Background

Youtube has forced logging in to watch embedded video in other sites, such as Reddit, years ago, as they say, to prevent spam use.

I’m not talking about how reasonable it is, but to fix a wierd problem, that I have already logged into Youtube, but still face problem watching embedded videos.

I am using Firefox in Windows 11.

tl, dr

Disable Firefox’s Enhanced Tracking Protection for every site that has embedded Youtube videos.

Just click the shield icon to the left of the address bar, and then turn off the switch.

Why?

Firefox has a strict privacy protect policy by default, to stop sites tracking you.

That disabled cross-site cookies, so, for example, Reddit cannot use Youtube’s cookie. In result, embedded Youtube will treat you as no logged in guest.

Chrome or Edge may have some familiar issues, but I did not test them.