Google is the main funder of Mozilla via search royalties and direct funding. It's easily changed...but in reality Mozilla suffers if you do change the default because they lose royalties. It's hard to be a good competitors if your livelihood depends on people staying with your competitor's services.

In 2014, Google paid most of the $300m or so of Mozilla's revenue.

You realize Mozilla makes good documentation but get how it has enough money to do so. They have too much money for what they do.