Please take a look at the contributions in the paper at the end of the introduction. The JVM uses operating system abstractions (like a file system, threads, and synchronous APIs) that were non-existent in the browser when the paper were published, and are still widely unavailable natively. Figuring out how to construct the functionality necessary not to just simply execute Java bytecode but to provide a full Java Virtual Machine, and then show how this could be generalized beyond a JVM, is a CS contribution. Disclosure: I'm a labmate of the author.