So, mission accomplished?

I disabled 3rd party cookies ever since the option appeared in Firefox, and never had any issues.

I disable 3rd party cookies too, but I've had several websites that have failed to work properly because of it. So now I've had to whitelist certain 3rd party cookies (e.g. accounts.google.com, payments.google.com, etc.). But since these domains are whitelisted, they can set their cookies from any website I visit. With the idea rlpb proposed, each website (and its permitted 3rd party cookies) would at least be in its own container.