This is why I loved developing for Firefox OS. Their simulator is really just Gecko inside a smaller window and with simulated touch events. You could do some amazing things, such as live-inspect DOM on a connected device and treat it as if it were a local webpage. And now the WebIDE built into Firefox seems to be even more pleasant. I even used to sometimes test the app in my Firefox browser, without bothering to connect a device or fire up the simulator. It was super-speedy.

I'm so sad Firefox OS is probably never going to properly take off. I use Android and like it very much, but development for it is a literal nightmare.