Firefox and "Custom element doesn't exist"

since one of the recent updates to Firefox (currently 118.0.2), I got the “Custom element doesn’t exist” problem.
Everything works great on Edge.

All the elements, that have this problem here, are installed via HACS.

  • RGB Light Card
  • Harmony Remote Card

I know that HACS components are not supported here, but just as info for others encountering this problem.

For me, that’s the final reason to switch to Edge and turn my back on Firefox…