Re: Definitions, please
And what counts as a third-party cookie? One set by secondary content, such as an image, from a different domain to the page it's in? Hmm, would that be *all* secondary content, or is a line being drawn somewhere?
Disclaimer: I didn't vote on your comment, so it's not me.
Third party is everything not the page you explicitly visit. So if you visit dailymail.co.uk, then dailymail.co.uk and web link with that name are the first party. Everything else being loaded on that page like analytics.google.com is third party. So it's not really a 'standard', but a simple rule. If it's first party, then let it load, else do not load.
It's also a simple rule to give some protection by forcing website to check their content instead of letting random third party putting virus everywhere. If you want third party content in first party website, simply put the content under the first party website. Obviously, the shady ones like ads and virus would avoid that, so the first party could never check what they are planning to put on the website.
What about user tracking that the user generally opts in to?
If the website had done it right, then it's just a matter of putting first party tracking cookies on the browser the user opts in, which would then track the user until it is deleted. If third party is blocked, then third party tracking cookies as well as third party content will be blocked from putting into the browser.