Ask HN: How did Firefox (Mozilla) land a deal with Google?

I'm assuming that Firefox gets money through searches performed from its default start page and through the search box on the upper right of the browser.

Two part question:

1) How did this deal come about? Is there a program for this type of affiliate search? (What I've found requires you use the Google watermark and traffic must come from your domain).

2) How did Firefox secure this deal? It seams like Google could just decline to pay any money, and Firefox would still be reluctant to use a different search. If users prefer Google anyway, what incentive does Google have to pay Firefox?