>> Google makes no money in the sell of either. Firefox and/or Opera could change their default to MSN if they so desired.
Sorry?! Let's get this straight: the Mozilla Corporation made over $72 million in 2005 from Google - if you search Google with the integrated search box Mozilla earn approx. 80% of the search ads revenue. Same goes for the default Firefox-branded home page.
Opera is no different - it is no secret that they dropped the ad banners in the browser and have moved to a "free" model because they have negotiated a similar deal to Mozilla.
Google makes plenty of money from these two browsers, Firefox in particular. It's not for nothing they pay $1 per installation of Firefox (via AdSense referrals) and advertize it heavily.