SAN FRANCISCO -- Microsoft's not the only big tech player taking a gamble on a new direction. Mozilla made an aggressive argument for Firefox OS to Web and app developers Monday night at its confusingly named Mobile Monday Mixer -- confusing because the company held the event last night at its San Francisco office.

As the lights from the Bay Bridge blinked in the background, Jay Sullivan, Mozilla's vice president of products, laid out why developers should care about Firefox OS. "If you're looking to build and develop mobile software without the 30 percent toll [Apple charges], Firefox OS will appeal to you," he told a room packed with around 75 developers. Among those present were HTML5, JavaScript, and CSS developers, as well as developers from at least one competing browser.

Firefox OS is Mozilla's stab at providing an open-source mobile OS alternative to Apple's closed iOS and Google's semi-open Android -- not unlike what Firefox did for Web browsers when it debuted in 2004. But Mozilla is also recycling software it's creating for Firefox OS in its desktop and Android browsers to improve them. At its heart, Firefox OS is an attempt to keep Mozilla relevant as the rest of the world goes mobile.

Sullivan told the crowd last night that Mozilla has created a way -- technically, a "payments API" -- for regular Web browsers to handle payments the way that native mobile apps do. He said that Mozilla expects this development to drive the creation of multiple app stores -- the exact opposite of Apple's single-store format -- and will allow developers to distribute their apps directly to customers.

"You can't do A/B testing in the iOS app store," Sullivan said, referring to the developer method of testing two different options with their users.

But that payments API alone won't cause app makers will flock to Firefox OS. Sullivan argued that the learning curve for any operating system that wants to compete with iOS and Android -- and, by implication, Microsoft's Windows Phone 8 -- must be easy for developers to pick up.

"No new ecosystem will emerge unless it doesn't require developers to learn a lot of new stuff." Firefox OS is entirely built on HTML5, JavaScript, and CSS, code frameworks that developers already know, he said.

Mozilla's director of research Andreas Gal didn't mince his words when asked what he thought of Windows Phone 8, Apple's iOS, and Google's Android at a demo of the Firefox OS in September. "Microsoft will be the last to experiment with proprietary native code. It will either fail and make Apple and Google the only two to have successful private systems, or it will succeed and it will take longer for them to go away."

Firefox OS's reliance on the Web is also its biggest weakness. "One of the great things about the Web is that it's open, scrappy, and you can build your own business model," Sullivan noted. But, he said, with a chuckle, "what's bad about the Web is that it's open, scrappy, and you have to build your own business model."

Others at Mozilla are also cautiously enthusiastic about Firefox OS's chances of success. CEO Gary Kovacs told me back in September that it was simply the next phase of the non-profit organization's goals. "It gets back to the overriding mission that Mozilla began 15 years ago. We did it with the browser, we've now seen the explosion of Web pages and value for the world."

Kovacs noted that there are 2.5 billion people connected to the Web now, and pegged Mozilla's success towards getting the next 2.5 billion online. Firefox OS, he said, will be "as disruptive as when we put out Firefox."

Gal made it clear that that even when the operating system is ready for the public, developers still will have to put in some effort to make their Web sites ready to use as apps. This includes icon creation, but he predicted that, overall, creating an app won't be that different from building a Web site.

"It's not so much about convincing people to build HTML5 apps, but to make content better optimized to run on mobile," he said. And while Kovacs conceded that Mozilla didn't do enough in the past to promote better performance standards, he contended that today is different.

Brendan Eich, the inventor of JavaScript and Mozilla's chief technical officer, said the Web is now powerful enough to do everything that a native app can do:

The web stack is strong enough as a programming model to provide really rich applications. Last year when we started Boot to Gecko on Github, we realized that we would have a thinner stack than the dominant operating systems. We also realized that the Web stack is never perfect, it's never complete. But the Web always catches up, and it has the broadest reach.

Last night, Sullivan described the birth of Firefox OS as highly unusual. "Andreas Gal started Boot to Gecko [the original name for Firefox OS] with nothing but a readme file. I've never seen such interest in nothing but a readme file."

Along with the appeal of coding in a language most developers already are familiar with, Carlos Domingo, CEO of Mozilla's first carrier partner Telefonica Digital, said in September that they are working on developer incentives. What those are and if they involve cash incentives, though, he refused to say.

We've known since the deal with Telefonica was announced earlier this year at Mobile World Congress that Firefox OS is intended to run on lower-powered phones, about as much juice as is required to run Android 2.2 Froyo -- an 800 MHz Qualcomm chip, with only 256 MB of RAM -- and Domingo said in September that the goal is to price them around $100 unsubsidized, the higher end for feature phones.

Gal reiterated in September that Firefox OS is more than Mozilla's mobile incursion. "This isn't the Mozilla platform, it's the HTML5 platform. The long term strategic goal is to have competing better implementations of HTML5, not just one."

Eich agreed that it's about upgrading the Web so that the browser can power a smartphone. "One of the brain twisters about Firefox OS is [what happens] when you have all the top Web engines able to run the same sites [the same way]. Hopefully, we won't be like the original Star Trek and get cancelled after the third season."