Don't know why, but Firefox on my Ubuntu is slow AF. Scrolling pages is just a pain. Graphics acceleration seem to be enabled.. Chrome is buttery smooth though, so no idea how to fix FF
Over here it is: Compositing WebRender (I have layers.acceleration.force-enabled;true and gfx.webrender.all;true)
There's a far less common problem where you are running firefox in XRDP or ssh -YC and it is being sluggish - for that you have to force-enable xrender https://bugzilla.mozilla.org/show_bug.cgi?id=1263222 )
* Running Firefox 93.0
*Update: I've rebooted my system, and it shows that my Graphic Card is now in use. Not sure which flag I enabled helped, but pages are buttery smooth as with Chrome. Many thanks!
Most likely just needed to restart Firefox. But glad you got it working.
And yeah, both Chrome and Firefox on Linux can be rather finicky with graphics cards due to high levels of unreliability in the past. Although the situation has improved over time.