Mobile phones running a new Firefox operating system will be available this summer in nine countries -- but not yet in the United States, Mozilla says.

Mozilla head Gary Kovacs said the June launch of Firefox OS phones would be targeted at emerging markets first and would be available in Brazil, Colombia, Hungary, Mexico, Montenegro, Poland, Serbia, Spain and Venezuela.

However, U.S. consumers will get a chance to sample a Firefox-based phone; Sprint already has committed to launching such a device and the first should arrive in 2014, Business Insider reported Monday.

Firefox OS is a Web-based mobile operating system similar in concept to Android, except all apps will run within a browser for a uniform experience across all Firefox-capable devices.

The operating system will be open source so carriers can add their own content on top of it, but a carrier can't lock it down and control it, Kovacs said.

"The Web needs to be unlocked for mobile," he said.

Alcatel, ZTE and LG have reportedly committed to manufacture low-end smartphones based on Firefox OS.