Some Xero products don’t work properly no matter what your browser is.
For me, Mozilla has bugs or weaknesses in Linux. YouTube chews my cpu (hardware acceleration is broken, at least for me). Tabs ‘freeze’ due to a bug in an X11 lib. Pop up bubbles (do you want to enable gps to this site type bubbles) if visible before switching workspaces appear on all workspaces but cannot be actioned and appear on top.
Mozilla as a company appears to be attempting poor monetisation models like attempting to build social networks etc. I would consider paying them a yearly fee if I thought they’d use money wisely, but at the moment executive appear more interested in vanity projects.