The current setting layout for choosing what data is deleted when Firefox is closed is convoluted. In the Privacy & Security tab, under Cookies and Site Data, there is a checkbox to delete cookies and site data when Firefox is closed. This is fine, however it is redundant as this exact setting can be found elsewhere on the same page. Under History, to the right of the 'Clear history when Firefox closes' checkbox, there is a settings button. This settings subwindow contains checkboxes for History, Cookies and site data, Temporary cache, and Site settings. The cookies and cache checkboxes are directly linked to the previous cookies and site data checkbox. Unchecking either of these will uncheck the previous box, and checking the previous box will check both of these, in addition to checking 'Clear history when Firefox closes'. This can cause problems because if you uncheck the box that says 'Clear history when Firefox closes' thinking it will stop history from clearing, this will also uncheck the previous cookies and site data box. This could be resolved by combining these to sections of the settings page or choosing to remove one of the sections.
... View more