I find the tiles highly useful, and Mozilla metrics show that so does a large portion of their uses.

I recently had to deal with a completely fresh Firefox and the empty tiles were quite annoying.

A few years ago a Mozilla engineer talked about advertisement and how ads should not annoy users but benefit them. His example was high-end fashion magazines, which people happily buy - not despite most of the magazine consisting of ads - but because the magazine was mostly ads. The ads are beautiful and tells you what style is in vogue.

Advertisement can be mutual beneficial.