Set privacy.sanitize.sanitizeOnShutdown and privacy.clearOnShutdown_v2.cookiesAndStorage (I don’t know if privacy.clearOnShutdown.cookies is still needed) to true.
To allow a website to keep cookies do CTRL+I on the address bar then check “Set cookie” in the Permissions tab.
Here’s how to auto-delete cookies without an extension: https://github.com/arkenfox/user.js/blob/128.0/user.js#L669
Set
privacy.sanitize.sanitizeOnShutdownandprivacy.clearOnShutdown_v2.cookiesAndStorage(I don’t know ifprivacy.clearOnShutdown.cookiesis still needed) totrue. To allow a website to keep cookies do CTRL+I on the address bar then check “Set cookie” in the Permissions tab.