That's unfortunately not an option for me, but I'm more than willing and able to run any diagnostic you want.

If it's better for you (and feasible on our schedules / timezones), we can even do it synchronously over IM.
Shoot me a mail (norswap on gmail) if you want to set that up. Otherwise we can keep using this forum.

Yes, as indicated both machines have Firefox installed.
Both are also up to date (Firefox 75).