Firefox is fine and quick as long as you don't need to use any heavy Google apps. Some people might even consider this a plus. For me, between work and personal use I'm effectively married to Gmail, Google Calendar, Google Docs, and Google Hangouts. Unfortunately that makes Firefox a non-starter for me. Not to mention Firefox's privacy settings trigger countless reCAPTCHA gates across most of GSuite. I get that this is not Firefox's "fault" and it's done intentionally by Google, but as a user it becomes my problem.
I really want Firefox to work for me and I'd love to drop Chrome, but last time FF made big noise about performance improvements I tried it out and Gmail was still unusably slow.