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)
but it still works. i tried setting it just now and the video loads immediately now, but interestingly, the rest of the youtube contents still takes a second to load. before it also took a second for the video to load; not enough to make me stop using it, but it was noticeable.