That's hyperbole.
Firefox was the first browser that made switching search engines or dealing with multiple search engines easy. Firefox was also the first to have usable add-ons for blocking invasive ads and trackers, always promoted as the best add-ons in their addons.mozilla.org. The pro-privacy culture has basically grown on top of Firefox.
I'm using DuckDuckGo on Firefox and I installed it on iOS too, because it makes it easier than Safari to deal with multiple search engines.
As for Google Search, people forget that Google Search is first and foremost the best search engine and most people expect nothing less. And when they tried switching that default to others, people bitched and moaned about it. Google is so far ahead of everybody that for the general population it has no competition. The same reason for why Apple cannot replace Google's Search and cannot build their own search engine, so might as well make some money off of Google.
This is not selling the users to Google, this is simply providing a good user experience by default. If anybody wants to help and fight this, then the first step would be to provide a better search engine. Don't get me wrong, I like DuckDuckGo and will keep using it due to privacy concerns, but for many searches, especially local ones, the difference is night and day. Not to mention that DDG is also dependent on Microsoft's Bing and it will be a sad day when Microsoft closes access to its APIs. Because apparently it's pretty expensive to have your own web crawler ;-)