Favicons for Mozilla
Perhaps this is the case:
Do I need to add special html for my favicon to be seen?
Yes, you can use the same link tag as IE (the <link rel="shortcut icon">) or you can also use <link rel="icon"> (optionally you can supply the mime type too: <link rel="icon" type="image/png" href="...">).
By default Mozilla does not look for /favicon.ico instead relying on the link tag. However a hidden preference will enable Mozilla to look for favicon.ico. We recommend using the 'shortcut icon' link tag for now (since IE does not support the icon tag yet).