Can't you just use Firefox instead of that disguised Chrome equipped with stuff you get from Firefox Addon page?

You can. You can also try out Ladybird or any of the Fx's forks.

I quit Firefox after a long ride because I got tired of slow loading times, and scrolling that I wasn't able to fix. No matter the settings it's still not as good as in Chrome.

Firefox is much worse in customizations in basics like keyboard and mouse controls