The same can be said for Safari. It doesn't surprise me that YouTube has inferior support on browsers other than Chrome/Chromium base. Likewise there are features in Safari that are exclusive to Safari.
I don't really consume HDR content through Youtube,so the Chromium relation doesn't have much bearing on my situation. Although it does make me sad that the only browser that really caters to what I want from a technical perspective is Chromium, I'd love to continue daily driving Firefox.
Some youtube videos have it now, but not really. I ripped all my blurays and have them hosted on Jellyfin for consumption which I prefer to use as just a tab in my browser than their dedicated player.