Sometimes if Firefox has difficulties updating your setting during an update, it will perform a Reset. This generates a folder on your desktop named Old Firefox Data. Do you see such a folder?

If you check the Options dialog, do you still have a Master Password set? This article describes that area of the dialog: Use a Primary Password to protect stored logins and passwords.

Are you prompted for the Profile Manager if you try to inspect the passwords in the Password Manager?

• Tools > Options > Security: Passwords: "Saved Passwords" > "Show Passwords"

If that isn't working then it is possible that there is a problem with the key3.db and signons.sqlite files that store the encrypted names and passwords in Firefox.
Rename the key3.db and signons.sqlite files in the Firefox profile folder.
You can add .old to the file names (key3.db.old and signons.sqlite.old) or move them to another folder to make it possible to undo the action.
You need to set a new Master Password after renaming or deleting key3.db and all currently saved passwords are lost.
If that has worked then you can remove the renamed files that are no longer needed.
Otherwise you can rename the files to their previous names (signons.sqlite and key3.db).

• http://kb.mozillazine.org/Password_Manager#Troubleshooting