You can't delete all cookies if you want to preserve some of them. You will have to let all cookies expire when you close Firefox and create an allow exception for cookies that you want to keep and only clear cookies manually and not via Clear Recent History. *Tools > Options > Privacy : History: [X] Clear history when Firefox closes > Settings *https://support.mozilla.org/kb/Clear+Recent+History You can also consider to access website in Private Browsing mode if you do not want to store data to disk form those websites. *https://support.mozilla.org/kb/Private+Browsing