The trick is figuring out how many users would use the Firefox search box vs would just enter google.com into the URL the old fashioned way (or would change the search box back to Google). I have no doubt Google is measuring that number and used it to guide their bidding.

My hunch is that Google is only breaking close to even with this deal (i.e. making $300M for paying $300M) and bid high just to keep too many people from trying Bing.

Plus, Google tends to act at least a little altruistic when it comes to the web [1] and may mind less being generous to Firefox.

[1] http://wikimediafoundation.org/wiki/Press_releases/Wikimedia...