It needs to have 1st-party cookies enabled in FF for all sites. Now you're setting cookies on visits that you might not have if you'd used a whitelister only. (I sometimes visit Google and YT w/out needing any.)

My buddy Cookie Whitelist has let me decide when I need them on temporarily for years. They're not auto-deleted until session-end, but since I've turned off access, doesn't matter.

I do like the cache-emptying feature. Decided to try what another writer suggested, turn disk and memory caching off.