For FreeBSD-related servers having anubis installed accepts my firefox even if I'm mimic'ing it as Chrome on Windows with user agent switcher, but Gnome sites doesn't. Stop mimic'ing allowed me to access Gnome sites.You're just lucky here... I still see plenty of times when a website works in one web browser, but not another, even in a Windows environment. I still have to tell people to 'just try a different browser, see if that works', and to ditch MS IE...
On the other hand, if I recall correctly, some sites hesitated to access with plain firefox, but mimic'ing Chrome on Windows allowed firefox to access.