I always just toss the favicon.ico in the root without needing to add any page coding. I just double-checked FF with a couple of my sites and the favicons are working fine (as well as in Chrome and IE 8). Note that my sites are rather old and undoubtedly far more simplistic than yours, but just thought I'd mention it anyway.
html - why won't favicon load in firefox? - Stack Overflow seems to have a few tips as well.