Mozilla previewed the first commercial build of its Firefox OS at the Mobile World Congress exhibition and congress, which is currently running in Barcelona.

The OS is being pitched as a better alternative for low-end smartphones in developing markets and is built around applications written using HTML5.

For any operating system, the availability of apps and support from developers are both very important. Mozilla said it doesn't need to build a new ecosystem for Firefox OS because it can take advantage of all the HTML5 developers already writing software. At Mobile World Congress, it demonstrated integration with Facebook and mapping based on Nokia's Here platform. Applications for the OS will for example be available on Firefox Market.

Considerable operator support underlines the desire for an HTML5-based alternative to iOS and Android, but the depth of commitment is unclear, according to CCS Insight. Success hinges on apps, attractive devices and operator subsidies, it said.

The real acid test for Firefox OS and its long-term prospects is the quality of the software itself and the user and developer experiences that it fosters, according to Ovum. However, it will be difficult to say whether it meets those needs sufficiently until we have seen retail devices.

"What is clear from the Firefox OS demonstration handsets that we have seen was that they are still some way from being market ready, being both slow and buggy," it said in a statement.

The first phones using the OS are all powered by Qualcomm processors and will be offered by Alcatel One Touch, LG Electronics and ZTE starting this summer, according to Mozilla. Huawei Technologies will also come out with products later this year, it said.

ZTE will officially announce its first phone in Barcelona on Monday.

In addition to the phone makers, 18 operators are also lining up behind Firefox OS, including América Móvil, China Unicom, Deutsche Telekom, Japan's KDDI, Sprint, Telecom Italia, Telefónica and Telenor. The operators will first launch phones in Brazil, Colombia, Hungary, Mexico, Montenegro, Poland, Serbia, Spain and Venezuela, they said.

Mozilla expects more phone makers and more markets to added going forward. The US market will have to wait until 2014, it said.