Mozilla/5.0 (Windows NT 6.1; WOW64; rv:22.0) Gecko/20130313 Firefox/22.0
OK, that one was probably a robot. But these from earlier in the month are to all appearances human based on both request logs and header:
Mozilla/5.0 (Windows NT 6.1; rv:20.0) Gecko/20100101 Firefox/20.0
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:20.0) Gecko/20100101 Firefox/20.0
Version >=20 is the browser equivalent of using five exclamation marks, isn't it :(
Detour to FF and Check for Updates-- which means "Download and install update even if your prefs explicitly say to ask first" results in...