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This post has been updated with information about Firefox OS’s launch at the request of Mozilla.

Mozilla is just a few months away from releasing its first mobile operating system and it’s still facing lots of skepticism, considering Apple(s AAPL) and Google’s(s GOOG) domination of the devices out there. Gary Kovacs, Mozilla’s outgoing CEO, defended the company’s move to turn the web into a third mobile operating system, one where people won’t have to choose apps over web content.

He’s fighting public perception that native development for specific platforms isn’t working the way it was initially promised with HTML5 development. Facebook,(s FB) which famously tried to embrace the open web with its HTML5-based apps, has said that was a mistake and re-embraced native development for iOS and Android. At the Dive into Mobile conference in New York City on Monday, Kovacs said when Facebook tried it the web was different:

“The web is much different today than it was two years ago,” he said. Important things have changed that make it easier for developers to work with the open web, including “much better GPUs on the device, better javascript performance, better APIs,” and more.

Kovacs said offering a third option is in keeping with the company’s ethos of openness, giving more options to more device users (and by definition, carriers). That means going to countries where Apple and Google aren’t as strong: the first Firefox OS devices countries will be where Mozilla and Firefox are known brands, and in the developing world where people are going to be buying their first mobile devices in the next few years. The first launch countries in June are Spain, Portugal, Brazil, Poland and Venezuela, Kovacs said.

The U.S. will eventually get Firefox mobile devices, and Sprint(s S) will be a partner — but not until 2014. “We have to get to version 2, version 3 first,” he said.

But whether it’s a developing country or ones with more established mobile consumer bases, Kovacs said he believes it can’t just be about two companies: “It’s impossible for me to beleive 5 billion people [coming online in the next few years] will get the same apps from one [app] store or one ecosystem.”

Update 3:36 p.m. PT: It sounds like Kovacs may have been getting ahead of himself — or at least ahead of the information his company wants to announce. A Mozilla spokesperson asked us to update this post with this statement: “As Mozilla announced on February 24th, the initial countries where Firefox OS devices will be available to consumers are Brazil, Colombia, Hungary, Mexico, Montenegro, Poland, Serbia, Spain and Venezuela. Exact launch timing is decided by and dependent on our partners.”