Google paying Mozilla hundreds of millions of dollars isn't exactly a charity. Google care very much about the complete and utter ubiquity of their search.

Using Firefox more will put Mozilla in a stronger position to negotiate a better deal, whether with Google or someone else. Worst that could happen is Firefox turning into some kind of boutique browser for connoisseurs willing to pay. That's uncompetable.

They might be able to raise revenue using other innovative methods eventually, but that won't amount to anything if we aren't using the hell out of their (very good) browser.