Firefox is not on par in terms of performance at all, at least on the Mac. I use it at home and at work but it just uses too much CPU for me to recommend it to anyone.
I end up having to stick with Safari as my resistance browser. (Which isn't so bad, actually. I feel like Safari is pretty underrated in these discussions.)
Chrome (v70): ~10% CPU
FF (v63): ~7% CPUIf you check on Bugzilla, there are many bug reports about it.