I also won't argue your point about calling the pre-installed search engines as ads--but they have a utility to them. The upcoming ads are going to have a hit or miss utility. Either I frequent that sponsored site, or I don't and find it to be a waste of space on my new tab page until it gets filled out by another site.

I think if anything, I'd just be worried that this is a slippery slope for Mozilla. These new sponsored site listings seem completely un-intrusive for now... but could it go further in the future?

That being said, I think the proposed ads are very tasteful, and it won't affect my browser use.

I personally take objection to ads when they take away from the usability of the product, when they are of a form that could be used to infect my computer, and/or when they are of a form that can be used to pass on data to third parties. (Un?)fortunately, this covers the majority of advertisements on websites: a large chunk of ads are pop-up, pop-over, are flash (both for battery life and exploits), redirect to untrusted websites (exploits), and/or use content hosted by third parties.

As such, my worry for this is: what happens if someone buys a spot that takes you to a page that exploits your computer then redirects to (for example) facebook? I hope that the bar (price for a spot) will be high enough to discourage this, but I don't know...