Mozilla's new mobile operating system, Firefox OS, has already shown its face on a handful of upcoming devices from Alcatel and Huawei. This time it's the turn of the imaginatively titled company Geeksphone with the 3.5-inch Keon smartphone. Aimed more toward developers wanting a cheap phone to test apps on, the Keon will be priced between $100 and $150 when it goes on sale in the next few weeks worldwide, making it the first Firefox OS phone available to buy.

If you've already seen our hands-on with Alcatel's One Touch Fire smartphone then you'll be instantly familiar with the Keon. They're almost identical, so much so that I struggled to tell them apart in our photos. Like the Fire, the Keon is a 3.5-inch device, wrapped in a bright "Firefox orange" casing.

The Keon sits very easily in your palm and its chunky, rounded back makes it quite comfortable to hold. It doesn't ooze the style and sophistication of Sony's Xperia Z smartphone, but it's arguably a lot more fun. It more closely resembles the colourful, curvy Nokia Lumia 620. Tucked into that orange back is a 3-megapixel camera and you'll find a microSD card slot on the device as well.

The 3.5-inch display has a 480x320-pixel resolution. That's far from the Full HD screens we're seeing on many new phones, but for the price, you really can't ask for much more than that. It seemed fairly bright, although colors didn't exactly seem to pop. I was only able to view it under the searing lights of the conference center so I'll reserve my judgement for the full review.

The Keon is running Mozilla's brand-spanking-new Firefox OS. It's open-source software, based heavily on HTML5, which Geeksphone COO Javier Aguera Reneses explained to me is less demanding of hardware. I sincerely hope that's true, as the Keon is only powered by a very weedy 1GHz processor.

Visually, Firefox OS looks a little like a cross between Android, with the multiple home screens, and iOS, with the large grid of app icons. It looks quite neat and fairly attractive, but without being able to spend a longer time with the phone, I'll have to again leave my final verdict for later. One of the problems it will face however is apps.

With developers already showing little enthusiasm for bringing their apps to a third platform after iOS and Android, it's unlikely they'll want to do it for Firefox OS. However, Mozilla reckons that the open nature of HTML5 on Firefox OS should mean that existing HTML5 Web apps can be easily tuned for phones. Whether that really is the case remains to be seen.

Again, the Keon is aimed mostly at developers, wanting a cheap and cheerful phone to build apps on. The benefit -- according to Reneses -- is that developers will receive updates to the OS within a day or so of them becoming available, rather than in weeks or months as is the case with Android. The Keon will be available for anyone to buy, though, developer or not.