Understanding how Firefox tracking protection works is one google button press away.
If you tell me that the OP had the time, patience, and technical skill to list all those possibilities but could not do a basic check on how Firefox tracking protection works, and instead talks about how with Firefox tracking protection "plenty of honest parts of the internet would break", and how blocked domains are used "sometimes for legitimate non-tracking purposes", forgive me for not buying the "openly unsure" claim.
As mentioned in my comment, I'm aware that tracking protection uses a domain block list. (I edited it about a minute after posting to make that more clear.) I did do some research, I just didn't link to it because the comment was getting too long.
I don't think a basic technical understanding is good enough to know how it plays out in practice. Computers are complicated, humans are complicated, organizations are complicated, and I've seen many cases where people jump to unfair conclusions because they oversimplified a situation. I think that hearing from people with experience (e.g. people who have worked at a company like CBS or people who worked on Firefox's tracking protection feature or something similar) is much more likely to lead to an accurate understanding of the situation than trying to work off of assumptions.
I've used Firefox tracking protection since it was release, and I definitely have had occasional issues with "honest" sites not loading. Not super often, but it's happened.
Then it's a good thing that the comment explicitly wasn't doing that, openly unsure of the likelihoods.