[TheLoneWolfling]

The pre-installed search engines are ads. They [Mozilla] are being paid to promote a product [Google Search]. That being said, it is not a form of advertisement that is particularly obtrusive, and it is "opt-out" - you are not prevented from removing search engines from the drop-down list if you so choose.

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...