In a blog post on Friday, Johnathan Nightingale as the VP of Firefox shared that they are no longer pursuing advertisements within the New Tab page. "[A lot of our community found the language hard to decipher, and worried that we were going to turn Firefox into a mess of logos sold to the highest bidder; without user control, without user benefit.] That's not going to happen. That's not who we are at Mozilla," he wrote.
Mozilla developers, however, will be toying around with other ways to make the New Tab area useful to Firefox users, particularly on new installations in coming up with web recommendations when there is no web history to analyze. With these new experiments they won't be pursuing an advertising model and they are going to ensure sufficient testing before pushing the changes out into the release channels.
You can find out more about the plans for the improved Firefox New Tab page via Nightingale's blog post.