Just logging into Gmail anywhere using IE means that your password is saved on that computer in a way that can be instantly retrieved. A simple program can be downloaded and run to find your password. Test it for yourself. If you're forced to use IE to check a Google account, make sure you go through the process of clearing all browser information.
This is not an issue on Firefox, but its not entirely IE's fault as Google could disable this and many other Google applications store their password in a totally insecure way. Firefox users should not save their password and, if they do, should set a master password.
Related: IE usage drops below 50% in the US.