I previously used Self-destructing Cookies which I liked but is no longer supported, and doesn't work at all in Firefox Quantum. Cookie Autodelete is an excellent alternative to the now defunct Self-destructing Cookies. It works brilliantly in Quantum and has fixed the cookie-related problems I had with Gmail under Quantum, for example. Quantum now works just like my previous version of Firefox, but faster! After another couple of weeks trial I will definitely contribute to Cookie Autodelete and would encourage all users to do so.