As Mozailla defines it, an open web app works in all modern browsers across the desktop and mobile. That idea thrills me as a user but gives me a sick feeling as a developer. Unless your app is fairly simple, that's a lot of platforms to target. What happens as the apps get more complex? I wonder how many companies will start with one or two platforms and then add support for more, once their code is tested and refined to enable "each browser to compete on app presentation, organization and management user interfaces."

I can't help but dream about an alternate universe where browser vendors standardized on one common, open source rendering engine and one javascript engine.