Firefox can store your website passwords, and you can create a master password to protect those passwords. Are you interested in one of those?

These articles describe which of the files in your personal settings folder (Firefox profile folder) have password information:

• Profiles - Where Firefox stores your bookmarks, passwords and other user data
• Recovering important data from an old profile

By the way, it might be easier to view passwords here:

orange Firefox button (or Tools menu) > Options > Security > "Saved Passwords" button