Just like everything else, if you don't pay for it then you are the product. It would be different if Firefox was funded by donations, but it is a for profit company that gets basically all its money from selling users to Google.
I really find it hard believe that
SELECT country, COUNT(*) FROM search_log GROUP BY country
is an invasion of privacy, or that somehow getting a commission off of the data you're already providing to a third party, is somehow making a user more of a product, than they already are.
Also, since they are funded by ads it means that they can't make ad blocking as a default feature, since then those users wouldn't be worth anything to sell. Whether you like it or not Firefox isn't free from any of this control.
Where are you getting your information, because I don't believe this true from my conversations with Firefox developers and data scientists. I think Firefox sends a ping to Google along with a telemetry ping to Mozilla, and then both Mozilla and Google correlate / fight over data as part of the contractual negotiations.
Why not pay roughly in proportion to the revenue you get from Firefox users searching?