I’ve moved on to EndeavourOS but I’ll just leave this here in case it’s useful to someone:
Firefox behaved extremely erratically when I attempted to watch a domestic streaming service. The site would be incredibly slow (like 20+ seconds to switch between pages) and would not play video.
Switching distros, I discovered that version of Firefox instead showed a little “enable DRM” button when visiting the same site, and after clicking that it’s now much faster and video plays.