Initial stock for the first Firefox OS smartphone - the ZTE Open - has sold out in a matter of three days, maybe to the surprise of many, given the youthfulness of the Firefox OS platform. The entry-level smartphone was first made available over the weekend on a "Buy it now" basis on Ebay for UK and US customers, costing £59.99 and $79.99 respectively.

ZTE nor Mozilla made it clear just how much stock was available in the first week of sales for the ZTE Open. Nonetheless, it's still impressive that the stock was cleared - as long as it wasn't 100 units or something similarly outrageous.

Pocket-lint first got its hands on the handset at the Mobile World Congress trade show in Barcelona in February. There's no arguing the ZTE Open is a budget smartphone, with a 3.5-inch touchscreen packing a low 480 x 320 pixel resolution and a Qualcomm MSM7225A chipset at its core with 256MB RAM and 512MB of storage on board.

The SIM-free phone is about as cheap as it gets for phones off-contract on the market today and that might be what is so appealing about it.

Not only does the ZTE Open let those interestedin  Mozilla's Firefox OS to get a taste and start developing, but it also begins a longer-term plan to create an open Web system to allow users access to the same apps across several different devices. Mozilla says apps will be compatible with Firefox OS, Firefox for desktop and laptop computers and Firefox for Android.

"Mozilla is dedicated to moving the Web forward as a platform for innovation and building products that people love," said Dr Li Gong, senior vice-president of mobile devices at Mozilla.

"We are pleased that now we will put the full power of the Web in even more people’s hands. With a great potential user base, we know that even more developers around the world will create their apps with new APIs to stimulate an inspiring new wave of innovation."

The ZTE Open was first made available in Spain, Venezuela and Colombia on the Telefónica network, before coming to the US and UK.

It's not clear when the next round of production from the China-based ZTE will begin. Could you see yourself buying the ZTE Open?