↓ここ　が参考になった
https://bbs.archlinux.org/viewtopic.php?id=281398

＞　The "HARDWARE_VIDEO_DECODING=blocklisted by env: Blocklisted by gfxInfo" shown in about:support introduced to Firefox when they renamed the VAAPI can be overridden in about:config.
＞　media.hardware-video-decoding.force-enabled=true

↓こんな感じ　radeonだけどね
https://i.imgur.com/h8t09IT.png