I've noticed that when using Facebook on Safari and Ubuntu (Firefox) the timezone defaults to US, when I log on with Win 7 (IE9) it resets correctly to NZT. I'm wondering if the is a security feature that blocks the browsers from accessing the localhost timezone or is Facebook has not implemented this for browsers other than IE?
Note: I logged on concurrently, Ubuntu first, then Mac (both had US timezone), then IE (NZT). When I refresh the view on the Mac and Ubuntu they now show NZT.