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?

This review is for a previous version of the add-on (0.3.4.6.1-signed.1-signed).  This user has other reviews of this add-on.

Hm, weird. My code doesn't contain anything 32 bit specific. I don't have a donation button, never thought about adding one.