Firefox's master password does not protect my web accounts
Solution 1:
From the mozilla firefox knowledgebase:
A master password will not prevent others from reading locally stored e-mails, reading your browsing history, or from accessing sites the browser is already logged in to.
You probably clicked "remember me" or some similar option on said websites. Cookies are not protected by the master password. That is why you are still logged in automatically on those websites. Firefox doesn't log you in, the website does.
How to fix this?
Log out on every website (always do this!), and never click "remember me" again. Just let firefox autocomplete the username/password field. You are now protected by the master password in Firefox.
Solution 2:
I'm using Rohos Mini Drive to password protect my Firefox profile. Once my Rohos disk is disconnected no one has access to my Firefox. (two thumbs up)