If you use "Clear history when Firefox closes" to clear the cookies when Firefox closes then all cookies will be removed. The same is when you use Delete browsing, search and download history on Firefox. You can only keep cookies that you have set as an allow exception if you let cookies expire if you select Cookies: Keep until : "I close Firefox".

See also http://kb.mozillazine.org/Cookies

thanks for the answer

apparently Firefox is lacking the functionality that I needed

here's what I need in steps:

1. I want to set Firefox to "delete cookies when I close Firefox", so I don't leave behind all the cookie garbage that I collect every time I web surf

2. I need a list that is called "do not delete cookies from these specific sites even if I close Firefox" so specific critical cookies that I need present at all times survive the "delete cookies when I close Firefox" cleanup

how do I submit a suggestion to Mozilla ?

If you remove all unwanted cookies yourself once and then choose to let all cookies expire if you close Firefox then you only keep the once which have an exception and the cookies that are used in open tabs if you have set to reopen tabs from the previous session. You can't use "delete cookies when I close Firefox" if you want to keep specific cookies. Even extensions can't override that setting and expiring cookies when Firefox closes is the same as deleting them that way, but does take exceptions in consideration.

yes, but what good is it if a cookie expired in a year from now ? what if it's a third party tracking cookie that I didn't want to have left in my system ?

with your suggestion I'll be stuck with many third party tracking cookies until the expire (which may be for a long-long time) only to save few configuration cookies that I wanted to keep

I should have the option to have the cookies, that are not listed in the "exception list", removed automatically when I quit Firefox if this option is not available, then that's Firefox drawback !!!

so, do you have a better suggestion ? do not suggest to un-check the option to allow third party cookies because then some web pages will not load

do you work for Mozilla ? is there a suggestion box where I could submit a request to add one more cookie option to Firefox ?

You only keep cookies after you close Firefox that have an allow exception. All other cookies will be removed if you let them expire if you close Firefox.

this is what I don't understand: how to force the cookies to expire when I close Firefox !!!!!

I have 3 options in Firefox 3.6.10 Tools>Options>Privacy_Tab

pulldown: keep until: 1. they expire 2. I close Firefox 3. ask me every time

if I choose #1, then I'm stuck with cookies that will expire in two years down the road, or so

if I choose #2, I lose all cookies

you are suggestion that there is such thing as #1 + "expire cookies at close"

where is that setting at ?

BTW, I have the allow exception on the Google cookies that I'm interested in