A subset of the tiles are paid advertisements. "Completely harmless" depends on your point of view. Personally, if I have a choice, I'll opt for the browser that doesn't show me "sponsored content" on first boot, just out of principle.
Mozilla's done a few other things that I mildly dislike, and they tend to clump together in my mind. Nothing that's a big deal, but enough that I usually keep a copy of Pale Moon on the machines I use most often.