Arguably, Mozilla's business model is built around getting people to switch to Firefox so they have leverage to make Google pay more for being the default search engine.
Firefox's market share has done nothing but decline for decades --- and Google still pays.
The fact that Mozilla are failing at their business model doesn't mean that's not the model.
So my argument stands.
Mozilla's current deal with Google is good through 2023 and is worth around $400-$450 million per year.
Every deal Mozilla has made with Google has payments increased --- even as Firefox's browser share has decreased.
https://www.androidheadlines.com/2020/08/mozilla-firefox-goo...
This article [0] from 2018 suggests an uptick, but it justifies it as "a deal to get paid for Google search traffic in parts of Europe" - so, actual market expansion.
I'm not saying you're wrong, only that I haven't seen evidence that you're not.
[0] https://www.cnet.com/tech/services-and-software/google-firef...
Google does not care about Firefox's market share. Google only cares that there is an appearance of competition in the browser market.
This is their own data on the matter... https://data.firefox.com/dashboard/user-activity
They've lost about 50 million users between 2019 and 2023 - roughly 20% of the 2019 totals.
In my opinion - Google pays because having a well known name that they can claim is still competing in the browser space is beneficial to them with regards to antitrust and monopoly laws. The ad revenue from the Firefox user base helps to make that cost manageable.