Mozilla is
introducing advertisements into Firefox, which they are calling “enhanced tiles“.
They recently parted ways with (dumped by) Google, who was funneling $300 million a year (90% of revenue) into Mozilla for making Google the default search engine. Now that this revenue is gone, I suppose Mozilla figures they can offset some of these loses by including ADs in the browser. They also inked a deal with Yahoo! to be the new default search engine.
It's supposed to be easy to opt out of these ADs but in my opinion, this is just another step in the wrong direction for a so called "non-profit" (cough). There is a large
discussion thread on the Fedora Devel List, in which many are urging Fedora to replace Firefox as the default browser. I agree with this move. Users can always install Firefox from the repos but it would not be the default.
Firefox is still the best browser for my purposes, but combine this with questionable GUI changes and other privacy/tracking concerns the user must "opt-out" of, I'm growing increasingly disenchanted with the Firefox project.