Firefox has a search box because it's helpful to users. Period. End of story. If it's not helpful to users, it'll go away or be replaced. Mozilla does not build features to generate money. Mozilla builds features to make the Web a better place for users and developers.
But that particular feature generates them millions of dollars and is their primary source of funding. It's not far fetched to imagine if it came down to it, issues surrounding it might be more complex than other UI issues.
