Mozilla making money? LOL. Google just sends them spare change, pretending to pay for placement, to have an alt browser to show to antitrust authorities. Third-party use of Gecko satisfies that too.
So if someone else makes a browser off Gecko, then that one can satisfy Google's requirements, minus the special agreements Mozilla makes for search data, and suddenly there is mo reason for Google to pay Mozilla any more..
If Google stop paying for Gecko to track Chrome, it will lose feature parity, become unusable and fall out of use, where they can again be accused of monopoly. It seem unlikely someone doing a wrapper UI on a browser engine can fund that sisyphean task.