I've been using it the past two days, and it's really just...not good. The idea is fine: introduce people to FirefoxOS without having them cut Android apps cold turkey. The implementation isn't, however, which probably has something to do with the entire "run an entire other graphics frontend powered by a web browser as your home screen".

Graphical glitches with the icons, being unable to use any of the bundled apps (Browser, Music, Gallery, etc.) because it just results in an instant crash, likely due to being out-of-memory killed, unresponsive gesture support (dragging from the side of the screen takes multiple tries, even after you figure out that's a feature and only way to go back).

The most important issue is definitely that if the home screen is unloaded, pressing the home button results in a 10 second long FirefoxOS booting process before you can launch any other app. If someone wants to start up Snapchat by pressing the home button and launching the app, but has to wait 10 seconds for your home screen to reload, you're dead in the water. This is entirely possible to be due to me using a fairly low-spec phone...but that's the entire market for FirefoxOS...