And then people will complain that Mozilla is nagging them for money. I doubt anyone likes the nag screen that Wikipedia pops down about 15 seconds into reading a page and it covering almost half the screen.
Wikipedia has sufficient marketshare to survive despite that.
The ads that mozilla shows are fairly privacy-friendly, much more than any other ads you'd find on most websites. That's an improvement.
If you don't like them you can easily disable them.