Is hardware acceleration enabled by default in Firefox? How to verify its state?

In about:support I can’t see for sure if the hardware acceleration is enabled on my system. Is it necessary to modify some about:config preferences (such as media.ffmpeg.vaapi.enabled to true) and launch Firefox with the MOZ_X11_EGL=1 variable (or similar)?

UPDATE: running intel-gpu-top may be enough to confirm on Intel systems (image copied from elsewhere):

image

I use the following:

MOZ_LOG="PlatformDecoderModule:4" firefox |& grep -E -v 'AudioTrimmer|Got one frame output|nal_unit_type'