I've read that Pale Moon worked well for someone; haven't tried it.

This new $4k laptop with a 4K screen (I like that duality :) ) is bogging down; opening a new tab in Firefox, or even, reloading a tab that I already had open, takes five to ten seconds. That's unacceptable, when Chrome takes less than a second!

And, I've started moving "a window at a time" over to Chrome (a bunch of Alt+Tab, Ctrl+Tab Ctrl+L Ctrl+C Ctrl+W, Alt+Tab, Ctrl+T Ctrl+V; repeat until all the tabs in the Firefox window have been closed) -- and Firefox is still behaving slowly! So, looks like it's a total migration in the near future.

Thanks for the upvote and agreement! :)