So if you've got Firefox remembering your credentials for passwords, and you know where that password file is located, how exactly do you change those credentials if you entered them incorrectly and Firefox doesn't re-prompt you for it... ? The credentials look encrypted.
3 Answers
Tools -> Options -> Security -> Saved Passwords.
You can change them there.
You can do at JonT and barrponto said, or you can usually clear the recent history, cache, active logins and cookies, log into the site in question and when you login, you'll be prompted to change update your information for that site.
It happens to me switching between my Gmail and Google apps all the times. It always wants me to update my info after the cookie expires or I clear it and login with the other account, but it works for a single account if you clear the info.