It's not a 64-bit issue Rated 5 out of 5 stars
I got to my office PC with Waterfox x64 and IdentFavicon worked fine. Same add-ons. It must have been an old add-on left behind in the about:config junk of Waterfox.
Don't know why Google Chrome users put up with crappy favicon support. I suppose they have eagle eyes for text rather than the favicons (Chrome loses even the assigned site favicons - and people keep complaining to no effect).
I'm glad we got that sorted out! :-)