Help Menu "Check for updates..." malfunctioning

When I go to the help menu there is no Check for updates... option. Instead there is a "loading" animation next to the words "Downloading Firefox 3.5.2." I have NOT checked for updates, but it automatically starts downloading. The download never says that its finished, but it has updated itself automatically when I restart Firefox. The weird thing about this is that I have disabled automatic updates under the Tools>Options menu. This is a portable edition running off a flash drive. This wouldn't be a problem if I didn't want to update to Firefox 3.5.2.