Is this about WebRender? If so, here you go: https://www.omgubuntu.co.uk/2020/07/firefox-enable-webrender...
What does "Compositor:" say for you in about:support?
gfx.webrender.all
layers.omtp.enabled
layers.acceleration.force-enabled
layers.omtp.enabled isn't used when WebRender is on.
I'm on Nightly so I should have it for some time already, but I'm not sure if it is on by default or should I tweak some value.