I don't understand why you are downvoted. Filesystem access is another big one! Chrome has the technological advantage and sports an enormous kitchen sink of features. One has to make the hard decision, work on a concept that will work only on one browser, try to cut corners with graceful (or crippling) degradation, or wait potentially a long time until a spec is standardized and implemented. The latter may result in others hitting the market sooner, so it is understandable why we end up with web-apps that function in a single browser only. Hopefully this improves in the future.