I have an iMac 2015 and a MacBook (the one with the slow dual core ultrabook CPU). I use the normal edition of Firefox most of the time. I've never seen Clickup or JIRA run faster in any other browser.

It may be related with your screen resolution, I agree that Firefox has serious performance issues on Macs due this bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1404042 [Poor battery life on OSX with scaled resolution]

nah i've had it too, granted it's on a 10 year old Xeon box I got for 40 bucks 4 years ago on an equipment auction at my work, but Asana and clickup are unusably slow, so when I last tried to switch for Firefox I'd just use them in a chrome instance ( where it was actually usable) ,the trouble was I would keep accidentally opening links etc in chrome and before I knew it I was using just the chrome browser.