If Google didn't pay for being the default search engine, or tried lowballing, someone else would make a deal instead.
The idea that it's some kind of a proactive antitrust defense is one of the more bizarre ideas that gets repeated on HN.
If you look at the situation in the reverse, what sense does it make? Why would you pay a direct competitor to exist when the amount of money you put in to them is an incredibly large majority of their revenue? Firefox continues to become more irrelevant, and the amount of their revenue they get from Google doesn't really reflect that trend.
I'm not saying the only reason Firefox exists is for Google to point at it. That doesn't mean it isn't a major one. It also is pretty clear to Mozilla because they sure keep trying (and failing) to find other revenue sources
One plausible reason is that Google is not a monolith: the entity paying the money is the Search division, which does not compete with Firefox. Chrome does, but Chrome is not a party to the deal. Search is interested in maximizing their own profit, not in maximizing Chrome's usage share.
> Firefox continues to become more irrelevant, and the amount of their revenue they get from Google doesn't really reflect that trend.
It is a revenue share deal. Firefox gets some specific (agreed) percentage of the search revenue from searches done via the Firefox search bar. If the revenue Firefox gets is stable despite reduced relevance, it is because the revenue is stable.
Relevance doesn't translate to revenue. What matters is the number of users and revenue per user.
This already happened with Yahoo. Mozilla got a ton more money, too.
It was utterly disastrous for them. It turned out that Firefox needs Google as the default more than Google needs them - well, for the stated purposes of the deal, of course.