[ArcadeQuarters]

Most important thing is to make sure the google toolbar is removed from any Mozilla-derived browser you choose. That’s where the money comes from.

[McGruff]

I've been trying to find out where Mozilla makes it's money. Came across this.

As Mozilla notes in its report, about 85 percent of its royalty revenue in 2011 came from its contract with Google. While Mozilla has similar deals with other search engines, including Microsoft’s Bing, it’s clear that the majority of Firefox users still prefer to use Google. “The receivable from this search engine provider [Google] represented 77 percent and 64 percent of the December 31, 2011 and 2010 outstanding receivables, respectively.”

http://techcrunch.com/2012/11/15/mozilla-releases-annual-report-for-2011-revenue-up-33-to-163m-majority-from-google/

So it does look like if you use their google toolbar they make money from that.