Edit: After reading the recommendations & arguments at arkenfox, I have opted to remove CookieAutoDelete as well as PrivacyBadger and CanvasBlocker. Instead I have:

• set Enhanced Tracking Protection to "Strict";
• setup uBlock Origin to level "medium";
• tweaked some extra about:config entries as recommended here and here, except for privacy.resistFingerprinting.

I'll also consider setting network.cookie.lifetimePolicy to 2 for having all cookies session-only (apart from whitelisted ones).

I observe a much faster loading of the pages now!

My preference is to immediately remove cookies from domains, as soon as (or just some seconds after) a tab with that domain is closed. Except some whitelisted domains specified by me.

To do this, I've used – for years – Cookie Autodelete. But I've discovered now that it doesn't work with Firefox's Strict Mode (the extension says "strict mode is not supported").

All in all I think my understanding of Firefox's capabilities and policies regarding cookies and similar extensions is outdated. I'd be grateful to anyone who can offer insights or links to well-informed sites about this.