Firefox blocks known trackers and isolates third party cookies per site. They do have legitimate uses, and not every site has made the switch to modern tech that could replace it.
Yeah my company uses them for integrating some of our apps together. They aren't used for tracking at all, and we'd be up shits creek if they were, because our (corporate) customers audit that sort of thing.
Because of Google we've had to create an alternative solution which has taken years to develop and is only getting deployed now. Those fuckers have way too much power over the Internet.