Because Mozilla promised us privacy, and “privacy-friendly” ad tracking is still worse privacy than not baking ad tracking into the browser in the first place.

I don't think "privacy" works in a way you snap your fingers, and bam, you have privacy, without any progress or stations in your way. Especially in today's web. Also, it's not just on Mozilla. On the contrary. I feel like Mozilla is the only "bigger name" in this market who tries to navigate in this shitstormy sea that is the web now.

Tho, it's just me, but it sounds much better if my browser handles all the tracking and data sharing business in a controlled manner with advertisers in a "privacy-friendly" way than no control overall (especially since it's Firefox and not Chrome/Edge), hoping only the other side would respect my preferences and requests.

But in the end, as I read other comments here, the problem is just the default state of the checkbox, got it. Feels a bit silly - in this particular case - but I can understand it.