I trust Mozilla more than some pirated content website or their user.
If you need that content more than you are afraid to be hacked and understand risks involved you are good to go.
People who are not aware of that threat need to be warned. Telling nicely does not work and people will click OK without reading.
Just as I wrote it is not fun and games and magic unicorns from internetz are not giving latest movies/programs for free.
Yes it is censorship, but as I wrote if you understand the risk and know what to do you will find your way to download it without firefox.
So it is not like this domain hosts one bad file and it got flagged, it is apparently more often if it "sometimes .. is .. lie".
On the other hand if you don't trust then those should be included.
Question is, does Mozilla trust google enough? Does Mozilla trust some random website where people host pirated content?
That is random article written by some random guy. Seems like he is more technical than average Joe, but he does not have any statistics to show why this behaviour was implemented. It just looks like a nag that he get his pirated downloads flagged by Firefox. It is backed up by bunch of people who also use it on /r/libgen. If they don't like it they can move to IE6.