Thank you for the screenshots, having them helps a lot in understanding the problem, that screenshot looks like BT2100 PQ (sometimes called HDR10) video being displayed as BT709 (which makes it washed out and dull). If you are up for filing a bug on...
So that we can dig into the problem more, it would really help to have the text of about:support (put that in your address bar to see this troubleshooting page) as there are several errors and config preferences that could affect how it is behaving.
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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.
