The unsaid part is that Google keeps Firefox alive so that they are not hit by anti-trust over in-browser search. That's why FF will always trail Chrome, its the designated loser. If it weren't for anti-trust, Google would have bought out Mozilla years ago.
You can't buy out an open source project. If Google bought it out and started messing with it, there would be an immediate outcry and Firefox would end up with the community fork winning out, just like it happened with MySQL and OpenOffice.
A browser would not do well as a volunteer driven open-source project. It is simply too big and too complex to be able to get by without full-time paid developers.
