I saw this article and thought it will also be a great feature for firefox.(sorry that it is in dutch) https://tweakers.net/nieuws/209720/brave-browser-krijgt-optie-om-cookies-automatisch-te-wissen-bij-s...
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Agreed this would be a good idea, as there are addons like Cookie Auto Delete that do this automatically plus additional features. Would be nice for FF to incorporate it by default.