According to the article, the ads in the New Tab page will be selected before Firefox knows anything about the user's browsing habits. So there's no guarantee t

According to the article, the ads in the New Tab page will be selected before Firefox knows anything about the user's browsing habits. So there's no guarantee that they will actually be useful to him/her. If they do turn out to be useful, that's merely by chance. Mozilla could try to ramp up the usefulness of the ads by selecting a bunch of popular sites like Facebook, Twitter and IMDb. But since those sites are already so well known, they won't have much incentive to pay for the privilege of being on the New Tab page. Many of them can already be selected in the Search bar. Useful ads need to be contextual, but contextual ads require tracking the user's browsing habits. As a result, it is very difficult to display useful ads while respecting the user's privacy as Mozilla wants to do.