Since you've mentioned it, Mozilla isn't touting to use XUL for "open" cross-browser apps - although XUL itself, unlike anything Metro, is open source and does run cross-platform. Mozilla is even deprecating the use of XUL for its new Firefox OS (Boot to Gecko) in favor of using pure HTML5 instead. Maybe MS can work together with Mozilla and come up with a common API?
Where did you hear that? everything I've heard is the exact opposite:
http://www.geek.com/articles/mobile/a-deep-dive-into-mozilla... >> Everything is HTML5 >> The core to the Boot to Gecko project is the web. Everything you see — right down to the power icon and network status information — is generated by and displayed with HTML5. The icons for the apps, the apps themselves, and the notifications the apps generate… all HTML5. Even the Dialer and the Settings for the device are handled this way.
http://en.wikipedia.org/wiki/Firefox_OS >> Firefox OS (formerly Boot to Gecko, B2G) is an open source operating system in development by Mozilla that aims to support HTML5 apps written using "open Web" technologies rather than platform-specific native APIs. The idea is essentially to have all user-accessible software running on the phone be a Web app that uses advanced HTML5 techniques and device APIs to access the phone's hardware directly via JavaScript.[2] It initially targets Android-compatible smartphones.
The difference is Firefox OS is building as much as they can (everything?) with HTML5, Whilst all Metro's advanced functionality is hidden behind proprietary APIs - The comparison of "open-ess" between the 2 is not even close.
Checking out the Mozilla Docs at https://wiki.mozilla.org/WebAPI it appears that these "privileged" APIs are extensions, as they should be. For example, navigator.fm.antennaAvailable is to control the FM Radio.
The only one talking about 'bad' is you saying it's 'not bad'.
Sure it is if those browsers are cross-platform. I doubt the Windows 8 APIs are cross platform.