Then they aren't doing a very good job of it.

>Firefox makes up about 90 percent of Mozilla’s revenue, according to Muhlheim, the finance chief for the organization’s for-profit arm — which in turn helps fund the nonprofit Mozilla Foundation. About 85 percent of that revenue comes from its deal with Google, he added.

https://www.theverge.com/news/660548/firefox-google-search-r...

Hot take: Google keeps Mozilla/Firefox alive through the default search engine placement (which makes Mozilla millions each year) so they don't get designated as a monopoly with their browser.