Till date I've found no difference between the stock FF and the one with the branding. I suggest, the default useragent should be changed to reflect a Gentoo system e.g. -- Mozilla/5.0 (X11; Linux x86_64; rv:14.0.0) Gentoo/2.1 Gecko/20120401 Firefox/14.0.4
Usseragent has been depreciated and will continue to produce the same results that upstream has expected from all disros