Action Retro 
Federico Damián Schonborn@ActionRetro
WebIDE also had the FirefoxOS Simulator built-in, so you could run FirefoxOS directly from the browser since the whole OS was indeed a big webapp running on top of Linux.
I used to play with it a lot. I even used it to communicate with my friends with one of the apps that were compatible with WhatsApp when my phone got stolen!
uhhhhhh@federicoschonborn @ActionRetro and if you want working webide today without too much digging, waterfox classic has it