Hi :) I had this problem. On the "TOOLS" - "OPTIONS" - "PRIVACY" menu you will see a drop down box, which like you said you have changed to "USE CUSTOM SETTING FOR HISTORY" Now on the page you have additional options. (If ticked) Below where it says "ACCEPT THIRD PARTY COOKIES" you can change options in the drop down box to: Keep Until "I CLOSE FIREFOX" I thought this would delete all cookies but it does not. To delete all cookies, tick the box next to: "CLEAR HISTORY WHEN FIREFOX CLOSES" then click "SETTINGS" to the right. Here you have lots of option about what data Firefox keeps/deletes. I ticked the "COOKIES" box. (choose your own preferences for other options) and now the cookies are deleted on exit for me. Your issue may be different and you may have already done this etc. I did not find the cookie options intuitive due to me not knowing there are different levels of cookies. Hope it helps someone :) r