Every time a user opens up a new tab in Firefox, the browser displays nine boxes -- or Tiles -- showing screenshots of his most visited websites. According to Darren Herman, Mozilla's vice president of content services, what Tiles display is currently based on an algorithm which combines your recency and frequency of visiting a site.
He says that the algorithm takes about a month of normal browsing behavior to update Tiles. Due to this the new-tab page is of no use for new users, and this is where the company wants to cash in.
This means that the sponsored Tiles will appear only to new Firefox users, or people who have re-installed their browser, and will be automatically replaced with content more relevant to the user after the initial 30-45 day period.