Check your extensions and privacy settings. Firefox is more aggressive in blocking trackers and that does break some authentication flows that involve trackers. You can always disable some of those protections to get the website to work, though I haven't had to do that in ages.

Other than that, Firefox on the Mac is consistently easier on the fans than Chrome, and unlike Chrome, I almost never get runaway processes.

Web pages are also as snappy as Chrome. If a page feels slow, I often open it in Chrome to compare, just out of curiosity. It used to be that Chrome would struggle less with these pages, but FF seems to have caught up in the past year or so.