The degree of protection very much depends on how strong your master password is.

When using a master password, the data is encrypted using Triple DES Encryption in CBC mode. This level of encryption is good for general purpose use. The weak point it the master password, if you have a weak master password there are programs available that will be able to crack the master password, they often do this by using a brute force method. If you use a strong master password, the brute force method will need a very long time to crack passwords. For details on password strength and creating strong passwords

see

• http://en.wikipedia.org/wiki/Password_strength
• http://luxsci.com/blog/security-simplified-the-basesuffix-method-for-memorable-strong-passwords.html

A master passwords adds an extra encryption level to the passwords that are stored in the Password Manager.
It doesn't have affect with visiting websites.

https://support.mozilla.org/kb/Protecting+stored+passwords+using+a+master+password https://support.mozilla.org/kb/Choosing+More+Secure+Passwords

http://kb.mozillazine.org/Master_password

I' m mosr grateful for your help for an uninformed beginner!

As someone who has administrated medical databases for 16 years I was asking the same question. I am shocked that we appear to be the only people asking it. Everyone should assess the risk the risk before they store passwords. Perhaps the answer is hidden a place I failed locate in the help.

I might add that there is always *some* risk. It is no insult to Firefox that I intend to hand it neither the keys to information entrusted to me by others nor those to my own most sensitive information.

Like you, I appreciate the replies. Thanks, people.