Fixed it! Rated 5 out of 5 stars
It worked on my 32-bit Firefox but not my 64-bit Pale Moon or Waterfox. This is the only extension or plug-in not to work with 64-bit. So I switched back to 32-bit because I can't live without Identfavicon.
Do you have a place to donate? I didn't see one?
Hm, weird. My code doesn't contain anything 32 bit specific. I don't have a donation button, never thought about adding one.