Week 3 Muddiest Point

I'm glad there was a detailed discussion of open source software because I was always curious about Firefox. It is worlds better than IE--takes up less space on computers, has support, more security, etc. The people who developed it must have been highly motivated, along with the people who contribute to it by developing all of the great add-ons and themes (Foxmarks being my favorite). I always wondered how something like this could be free. Does this mean that the developers don't make any money from it or maybe they do from advertising or something? Perhaps this is a goofy question, but I really am curious and am surprised that these developers who make open source software that is so great are doing it for no monetary compensation.