Hello, of course i have my password vault locked with primary password.
Unfortunately, remembered logins on websites like Google and Facebook are secured by cookie login. Which not require my primary password. This is convenient for daily use because I don't need to enter their passwords anytime I open the browser. But when someone uses my computer unsolicited, this person gets instant access to my GMail/Facebook.
This could happens at work, because office PC credentials are in charge at IT administrator, which could use my PC in case of support/installation/updates/etc. In these cases he can open Firefox and use my Google/Facebook account without entering any password.
So I suggest to add a Firefox option in order to allow user to protect also cookies login data under Firefox primary password (which is only known by me). In this case, without knowing the primary password, nobody but me will be able to use my personal accounts.