I have seen folks talk about a pain point for using FF (or forks) being related to YouTube being super slow. The about:config settings the article mentions did seem to lead to YouTube loading faster on both my FF and Zen-Browser installs. So maybe this might help for others that specifically don’t like to use FF as their main browser because of YouTube.
For those that just want the settings:
gfx.webrender.compositor.force-enabled (set to true and restart FF)
If on AMD GPU, this extra setting is supposed to help reduce CPU usage:
media.wmf.zero-copy-nv12-textures-force-enabled (set to true and restart FF)
*edit - per Zak in the comments. The AMD setting is Windows specific.



Word of warning, I did this (gfx.webrender.compositor.force-enabled) on my Tuxedo OS system with Nvidia and I don’t know if it was just the next time I started Firefox or because said restart was after a big system update, but Firefox crashed on launch every time until managed to get it into safe mode (wasn’t as easy as holding shift) and then turned this back off.
I wonder if more people in testing have had issues with it like you did. Might explain why it is default false. Though it is good that you noticed that it happened after a big system update. Did you happen to notice if your Nvidia drivers also got updated along with the other system stuff? I am not a dev, coder, or anything that would give me special knowledge (just curious). Maybe the GPU or X11/Wayland might be the cause (also could just be with how FF was calling resources).
I hope that if others run into the same issue (or similar) will share here and on any other places where the settings have been shared. Not that I expect Mozilla to see them, but could be helpful for folks to know that they might need to change it back. As it is very easy to not have issues for a while and not remember even flipping a setting if something breaks. Would also be interesting to see if issues are any more common depending on the GPU and/or the windowing systems (or OS if Windows, Mac, and BSD users also run into issues).