But how do you even know which origins are trackers, as a site owner? I know that social networks like Facebook and Twitter are, but what about GitHub? I guess,

But how do you even know which origins are trackers, as a site owner? I know that social networks like Facebook and Twitter are, but what about GitHub? I guess, one way to find out is by viewing your site in Firefox w/ Tracking Protection enabled, and checking if any requests were blocked.