I am on the latest version of FF on Linux and I don't have HDR working, not on YouTube, nor on standalone players like Jellyfin. Yes my display is HDR and Wayland+gnome is exposing HDR properly to games and Helium (chromium fork).

Since some govt and utilities sites only work on "chrome" (borked even with user agent switcher set to chrome+win on FF) I had to get this other browser, and the speed difference is noticeable on most sites, even tho theoretically FF should be faster since its stripping a lot of crap with uBlock Origin.

Tried flatpak'd Brave and also runs snappier than FF.