I think what parent poster was referring to is not the source of the money but the reason:
Much like Intel has cross-licensed patents with AMD in order to keep their competition viable enough to stave off monopoly and anticompetitive business practices accusations, it could be argued that Google’s promotional search agreements with Mozilla for Firefox are more to Google’s benefit than to Firefox’s.
What does it matter if Google avoided an anti-trust suit?
What matters to me and (I bet) other consumers is that we have a good browser that isn't Chrome. One that tries to keep Chrome honest when it comes to web standards. Consumers actually have increased choice, we're in a better place than we would be if Chrome was a monopoly. If that helps Google avoid anti-trust scrutiny in this area, fine by me.
The comment thread we’re both replying to implied that Firefox couldn’t exist without the Google money, which is disingenuous, because Firefox existed in its various code rebases, and under former Mozilla brand names, long before the Google money came in. Mozilla would have to make some tough choices, but Firefox would be maintained by volunteers independent of Mozilla if necessary. Mozilla isn’t Firefox. Maybe the Google money benefits Mozilla more than Firefox, and more than it benefits Firefox users.
For now, Firefox still has the edge on features which enhance user privacy[1], so I hope to see a project like OP for Firefox and Edge soon. More choices is a good thing.
Mozilla used to do just fine in making their browser before the hundreds of millions of "Google doesn't want an antitrust suit" dollars............