I don't want to delete cookies by default (since I don't like to lose my shopping cart due to accidentally closing a tab in a shop I haven't used before), but I certainly would like to be able to ban sites that use cookies in a user-hostile manner from storing cookies permanently.
It would be even better if Mozilla used the voluntary telemetry + manual user feedback to decide which sites benefit from cookies (e.g. web shops), and applied this to everything else (e.g. news sites).