One could also argue that Apple has benefited the most from free software. KHTML and the various BSD flavours are just a couple of examples. They definitely "take" more than they "give".

what bothers me the most with firefox is that the UI never feels right, not under windows, not osx and not GNU/Linux. i know K-Meleon, Camino and Epiphany (and probably a lot of other gecko based browsers) exist for different platforms, but it would be a lot better if the official firefox builds used the system's native widgets. i know that the osx version of firefox 3.0 is planned to use cocoa widgets, what are the odds of this happening for GNU/Linux (gtk) and windows builds as well?