Can Firefox Browser Passwords Be Protected?

I going to have someone stay over at my house and they will also be using my computer, which means they will easily be able to access my passwords from Firefox. Is there anyway I can password protect that option so that the passwords can not be seen by anyone else?
Go to Edit > Preferences > Security > Click on "Use Master Password" > Set a password.

As far as I know after a master password is set Firefox asks for the master password every time you want to use the stored password.

Remember if you have select the option "stay logged in" in any site the need for password recall is not necessary. To get rid of this issue delete all your cookies, cache, saved sessions etc.