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.