EDIT: Ignore my blind confidence. CAD is (mostly) broken in recent FF versions. (See ivn’s reply to this post).
Consent-o-Matic with Cookie Auto Delete and Firefox’s Multi-Account Container tabs covers it all nicely for me.
Cookie banners get handled, cookies I don’t explicitly want to keep automatically disappear when I leave the site/close the tab, and those I do want to keep can be given their own containers to keep them separated.
You’re right. I’ll be damned. That’ll teach me to set-and-forget then not keep up with changes to Firefox and their effects on extensions. Thanks for the heads up.