The new Firefox Developer Edition looks like a nice tool for those of use building Web Apps with Xojo.
Firefox Developer Edition Built for those who build the Web
Happy coding! 
The WebIDE is also built in to the standard edition of Firefox if you want to give it a try without installing the Developer Edition. Go into about:config, search for webide and double click the setting to enable it, once you’ve done that you’ll then find WebIDE in the Developer menu. If you’re developing for mobile you can also install Firefox OS simulators to give your web apps a test run.
I really like the Developer Edition though, as well as the dev tools I love the dark theme and the minimal chrome. All Mozilla need now is a visual drag-and-drop UI designer and a submit-to-market wizard built in to the IDE and Firefox OS will have a really top-notch SDK.
There’s some great HTML5 APIs for smartphones now - AppCache, WebGL, geolocation, device orientation, battery status, network information, page visibility, fullscreen, IndexedDB, web sockets, vibration, getUserMedia, WebRTC, …
Thanks for the tip!