GP claims that FF performance is terrible, which I cannot endorse (I guess GP might be having an actual issue), but I'll make a different claim: performance is not as good as Chrome (or maybe even Safari), despite all the accolades of FF Quantum, and my myriad attempts to switch to FF. The (at least perceived) inferiority of performance in addition to general UI ugliness makes it a no switch for me.
P.S. macOS 10.13.6.