Right now it's already set as the default search engine and you have to work to change it to something else as I understand it. I'm proposing that no default is set and that the user is asked to select one upon first installing Firefox from an ordered list of search engines. If that's already the case (it's been a while since I installed Firefox from scratch), then I'd argue that's fine. And it allows other search engines to contribute to be higher up in the rankings.

I can't think of anything that would replace the revenue that Google pays Mozilla that sustains the development salaries to hopefully keep Mozilla competitive and hopefully making it the best performing, convenient and private browser.