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Perhaps, but do you necessarily want to whitelist the entire site and all the accompanying JavaScript, or just the top level domain and a few components to allow it to work correctly. Depends on the granularity you desire. That's where uMatrix would come in handy.

Indeed. I'd imagine I could have it "trained" (to cover the 20 or so sites that make up the majority of my browsing) in just a couple of hours and it would be time well spent.

I'd even donate or pay for an extension that did this.

RequestPolicy Continued https://requestpolicycontinued.github.io/ does this, and comes with a subscription usability whitelist for CDNs and such.