Sorry no, that thinking is patently false right there. So everything that follows is compromised.
Advertising has been made a major driver, actually the only driver. It does not need to be a major driver and certainly not the only driver. And, spoiler alert, it cannot continue being a major driver.
Yes, advertising is a big and varied business with at least one century of storied successes (and how exactly it is done can range from the outright immoral to various shades of ethical). But society and the economy is much, much bigger than advertising. They can easily fund (and do so continuously in a vast range of domains) the infrastructures they need to function properly.
The internet is not a platform for ads. Its the digital canvas on which pretty much all of current life unfolds and will do so even more in the future.
Some sort of digital advertising business will be happening in the market driven / consumerist societies that are the current form of socioeconomic organization. But it is parochial, backward looking and eventually a dead-end to continue ignoring the much more fundamental role of internet infrastructure.
If Mozilla wants to continue being relevant (as I currently write this on a firefox browser, I surely hope they do) they need to escape the adtech black hole and its reality distortion field.