Using standard HTML 5 web language, Mozilla says its system will be able to operate on more basic devices than current smartphones.
Phones using the new system will appear this summer, starting with Brazil, Colombia, Hungary, Mexico, Montenegro, Poland, Serbia, Spain and Venezuela.
Speaking at Barcelona's Mobile World Congress, Mozilla boss Gary Kovacs revealed high hopes for the new system.
He said: "Our goal is to level the playing field and usher in an explosion of content and services that will meet the diverse needs of the next two billion people online."
Experts have praised Mozilla's early efforts in getting networks and manufacturers on board, but there are concerns about how willing developers will be to produce apps for the new system.
"Developers, which are often small operations, will not want to spend their time developing and supporting applications on several platforms," said Mohssen Toumi from analysts Booz & Co. "Especially if one of them has only a small share of the market."
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