By setting the master password in Firefox we can prevent easy access to our stored passwords. This is one of the methods how we can improve our protection.
If you can't copy files that are bigger than 2 or 4 GB, usually HD movies and such, on to your USB key, it's usually due to the file system the USB key is formatted to.
If you have activated the option to store passwords in Mozilla Firefox, than you can easily look at all password you have entered when you were browsing websites.