May I ask what exactly do you modify on Firefox? Don't think I ever fully went over settings etc. I could possibly just disable some extensions to see if that helps with the delay and resource hogging.
Well, Firefox has "hidden" settings in the about:config. Some of those can be changed to improve privacy, but they could have some drawbacks, like how one setting could make some images not load and such. Before I (temporarily, at least) switched to Brave, I followed the recommendations from Mental Outlaw
Don't think it really improves performance though, it's mostly privacy-related settings.
If you follow the steps from his video, you shouldn't have to manually change things in about:config, although you pretty much have to redo most things(logging in, reinstalling extensions, and such, since you're switching profiles). If something strange happens, you might have to jump into about:config and experiment a little.
Disabling some extensions could speed up Firefox, but it might only result in a miniscule difference in performance, unless one or more extensions drag down the performance.
If you were to follow the steps in the video, you could essentially ignore what he does when installing the profile(unless you're using Linux), and instead follow the written instructions.