If you use Firefox as your browser, your default search engine is Google. This means two things: 1) there’s probably a search bar on your browser, and that bar probably says Google on it and 2) your default homepage has a Google search bar in it. Like so.
Evidently, Mozilla, who manages Firefox was in a position to get a 3-year contract from Google for $300 million per year so long as they continued doing things the way they have been. And apparently this is pretty much the only way Mozilla makes money. Like, upwards of 90% of its revenue in recent years.
This may seem like a fucking ton of money to spend on something that people can easily change (i.e. their homepage), or at least it might until you realize that until this year, the number one browser in every previous year has been Internet Explorer or some other Microsoft offering. Internet Explorer has historically been terrible, but because of its status as the default browser with Microsoft operating systems, it has at times controlled the market to a somewhat anti-trust-inducing degree despite having a bad product. But still, it’s narrowly in second place despite its reputation as the number one browser for downloading a better browser. Ironically enough, its Google’s own browser, Chrome that is now number one and cutting into both IE and Firefox.