In December 2015, Mozilla announced it would be abandoning Firefox OS as a smartphone platform. Many assumed the company's withdrawal would kill any hope of a mobile operating system built around the open web, rather than a combination of native apps and tightly-controlled storefronts. In the last few years, plenty of "alternative" smartphone platforms, including Ubuntu Touch and Windows 10 Mobile , have faded into obscurity, too. Jolla has struggled on with Sailfish OS , but it's never felt like a true challenger to the Android and iOS duopoly. Three years later, a surprising competitor has emerged: KaiOS . The relative newcomer, which makes feature phones smarter, is already running on more than 80 million devices worldwide. How did it grow so big, so quickly? With a little help from Firefox OS.