A Firefox profile stores all personal information such as bookmarks and passwords in it. Everyone who is starting up Firefox with that profile is able to use your saved passwords and cookies as well which is a security risk if you ask me. One way to overcome this would be to protect the Firefox profile folder by moving it to a location that is not accessible to anyone except you.
I did this by moving the profile to my encrypted hard drive. The hard drive is encrypted using True Crypt and the profile can only be accessed if I provide the security key to decrypt the hard drive. Other means are theoretically possible as well, use a portable device that has to be plugged in before you can use the profile.
