I don't work for Mozilla, don't use Firefox, and am not a front-end developer (I write C). That said, I agree 100% that Apps of the future will be delivered over HTTP to general purpose runtimes that will essentially be browsers (maybe they'll drop the need to wrap everything in chrome, or something).

Browsers are increasingly become a dynamic language runtime attached to a powerful graphics rendering library. Make the runtime faster, provide better graphics widgets, and get past this "remote everything with shitty local caching" thing and you've got yourself one hell of a toolkit.