A week after, Deutsche Telekom has become the second.
The German company will begin selling thewith in Poland starting Friday in 850 shops and online, the company said Thursday.
Deutsche Telekom subsidiaries Magyar Telekom in Hungary and Cosmote in Greece will begin selling the phones starting in the fall. The company didn't release pricing details.
Firefox OS is a browser-based operating system that runs Web apps, which gives it a running start when trying to attract developers. Although it can handle Web sites and apps on its own, Firefox OS benefits when developers adapt their software with support for newer mobile browser technology for actions like handling multitouch input and gathering data from a phone's accelerometer.
With Firefox OS, Mozilla hopes to break some of the ecosystem locks of iOS and Android that can confine customers to interlinked hardware, operating systems, app stores, and services. Mobile network operators and handset makers -- and there are many -- see it as a way to push back at the dominant companies in the market.
"With Firefox OS we are expanding our existing portfolio with a new operating system that is open, developer-friendly, and reasonably priced," said Claudia Nemat, a Deutsche Telekom board member for Europe and technology, in a statement.
Firefox OS is found on lower-end phones right now, aiming for cost-conscious buyers upgrading from feature phones, but Mozilla hopes to extend to higher-end markets later. And it says Firefox OS will be available in the U.S. in 2014.
Though Mozilla has won over some allies to the cause, the operating system faces formidable challenges in denting the dominance of Apple's iOS and Google's Android.
in July 2012 along with Sprint, Telecom Italia, and Telenor. Since then, .