The browser is for browsing the Internet, it is a tool specialized for that, it has nothing to do with being an operating system. Being able to boot an OS within it does not make it an OS either. It just adds an unnecessary and potentially detrimental (to both performance and security) layer: OS -> browser -> OS, which is just silly. If you do not see the absurdity, let us consider this: OS -> browser -> OS -> browser -> OS, ad infinitum. :P
