Not sure its necessary any longer, "From Firefox 87 on, Mozilla will trim the referrer automatically for all cross-origin requests, e.g. requests from Site A (example.com) to Site B (secondexample.com)." https://www.ghacks.net/2021/03/22/firefox-87-to-limit-the-referrer-for-all-cross-origin-requests/

So far so good.

Impressively efficient on CPU and memory.
Might be a good idea to have a remotely hosted and updated default whitelist for sites it breaks, like Smart Referer does. Something like this: https://github.com/crssi/Firefox/blob/master/POOP-Exclusions.txt

Very good but I can't read the text with dark theme !!!

This add-on breaks Reddit for me (videos and gifs wont play). It works fine otherwise.

POOP constipates the companies that track and traffic in your online life. It blocks a widespread and previously unaddressed tracking vector -- Cross-Origin Resource Sharing. CORS is supposed to keep you safe, but websites & their data-tracking partners have weaponized it against you. POOP stops the abuse without sacrificing the security benefit of CORS when it's used for its legitimate purpose. You should install this extension if you care enough about your privacy to block third-party cookies and use Firefox's anti-tracking preference. POOP fills a hole in your privacy wall. Thank you, claustromaniac.

creating this add-on was a Totally Unanimous Righteous Decision - love it!