That glow I think you're referring to is "theater mode" and fortunately it can be disabled on the gear menu. It's incredibly distracting, especially in Firefox it can sometimes be laggy.
I think you mean "ambient mode". Theater mode is like the halfway point between normal-size an fullscreen-size.
As an aside, does anyone know of any good YouTube settings extensions? I usually open YouTube in incognito tabs to avoid the personalization "features", but this means none of my preferences around ambient mode and "stable volume" are saved.
As an aside, does anyone know of any good YouTube settings extensions? I usually open YouTube in incognito tabs to avoid the personalization "features", but this means none of my preferences around ambient mode and "stable volume" are saved.