Don't try to build a house out of this argument, because the wolves are going to blow it away.
If the top search engine spot in Firefox would be so valuable, than there would be real bidding wars. $400M/year is nothing when it comes to BigTech. Frankly, anyone could pitch a business plan for an investment bank to get a few billions and outbid Google. If anyone cared... but being the default search engine in a browser that virtually nobody uses isn't worth a lot. But it's a fantastic decoy, if you have nothing better.
(Also, Yahoo offered more when both Firefox and Yahoo still mattered. Which is not the case anymore. The only viable search engine today is Bing, who stopped caring about search, as AI seems to be more lucrative for them. Marginalia is also here, but that guy has less money than MS, prolly)
Safari exists exclusively on iOS and MacOS. On Android, Windows and Linux Chrome has virtually 100% market share.
Do you know why Google spends more money on Safari? Because on that platform they want to be the default browser. Safari doesn't depend on Google at all. Not like Firefox.
Firefox dies in 2 minutes once Google decides that it has outlived their usefulness, at which point all their users default to Chrome, where they don't have to pay to be the default search engine. And at the point they would have to pay only Safari, without any negative impact on their search traffic. But as it stands today, they would have no competitor on the vast majority of the consumer computing systems.
>Don't try to build a house out of this argument, because the wolves are going to blow it away
The core of my argument is that Google isn't stupid enough to risk their search monopoly just to prevent a browser monopoly, and you haven't even addressed that.
>If the top search engine spot in Firefox would be so valuable, than there would be real bidding wars.
There is a real bidding war, that's where the price Google pays comes from. The reason they don't get more is as you say, virtually no one uses Firefox.
>Also, Yahoo offered more when both Firefox and Yahoo still mattered
Really? In 2015 both Firefox and Yahoo probably had double their current user base, but that would still make them fairly insignificant players. Yahoo search had already been powered by Bing for years.
>Do you know why Google spends more money on Safari?
Because Safari has at least ten times more users than Firefox.
I don't know why you think there needs to be more to this than "a person's default search engine is a valuable commodity that Google will pay even their competitors for."
I upvoted your comment for the comprehensive reply, but I think @marginalia_nu[0] would laugh at you for putting him in the same category as Yahoo/MSFT...
From my understanding he's very much indie just like Marginalia is.
Except Safari, which they already spend far more money on then Firefox.
And if Google wouldn't pay, some other search engine would. We've seen it before, when Yahoo offered more money than Google.