Mozilla is hardly unique there. Webkit and Chromium are also open source and Google is pro-Web as well.

The only real advantage Mozilla had was the technical advantage of having one of the few popular and mature browser engines available of which only their programmers knew well enough to work on. Since Webkit though, that advantage has disappeared.

You could say their image as a non-profit out to do good is a advantage. Maybe that is something they should work on.