Previously in 152 you had to set a pref (gfx.color_management.hdr) to enable HDR video, and it worked only on certain hardware (most AMD, some very recent NVIDIA, nothing on Intel).Firefox 153 beta (and 154 nightly) should provide HDR video with all ...
Firefox Nightly (available at https://www.firefox.com/en-US/channel/desktop/ ) and Beta (available at the same site) now has HDR video playback, let us know if you give it a try and have feedback, if all goes well it should go to release in 153.
