That could change soon, as Facebook throws its massive social gaming weight behind HTML5. Because now Facebook, in addition to declaring its public support for HTML5 as a way to unite development across desktop and fragmented mobile platforms, is evangelizing that social game makers use HTML5 instead of Flash.

Cory Ondrejka, the former CTO of Linden Labs who joined Facebook when it bought his start-up Walletin late last year, wrote a blog post and gave a tech talk on the topic at Facebook HQ last night (hat tip to GigaOM). Ondrejka wrote:

With wide adoption and industry support, HTML5 will transform desktop and mobile gaming, creating amazing user experiences that are only a link away. Already, over 125 million people visit Facebook using HTML5 capable browsers just from their mobile phone, and that number skyrockets when we add in desktop browsers. The future is clear.

HTML5 games will (ideally) behave the same way across desktop, mobile and console platforms. Today, developers have to choose. (Adobe does offer Flash support on mobile, but some phones, notably the iPhone, don’t support it.)

For instance, most Zynga games are still exclusively released in Flash on Facebook. The company says it’s a matter of prioritizing development resources.

Meanwhile, it takes quite awhile for a game like Angry Birds, which is successful on one platform (in this case, iPhone), to launch on Android and other mobile OSs. And that annoys users because they can’t play their favorite games everywhere, or at all.

But HTML5 is not totally ready for the task. HTML5 browsers have varied abilities and levels of performance, and existing HTML5 games “often exhibit quirks and low frame rates,” so Ondrejka and his Walletin co-founder Bruce Rogers built a benchmarking tool that “exercises browsers under game-like conditions to measure how many sprites can move around on the screen at once.”

That sounds suspiciously like Facebook is building its own gaming product–if only for testing purposes–so Ondrejka was sure to state in his post, “Is Facebook Making Games? Definitely not.”

Ondrejka concluded that browsers are indeed inconsistent when it comes to rendering game elements in HTML5. “We want to help,” he said, since developers who master HTML5 will have much more versatile skill sets, rather than just excelling at one platform.

Plus, enabling multiplatform games works to Facebook’s business advantage, as app makers who use HTML5 will be less likely to ditch Facebook for the often more lucrative iPhone, or the increasingly widely deployed Android.

And that means more games on more devices for everybody.

Please see the disclosure about Facebook in my ethics statement.

Make the right impression. Your avatar’s appearance should be reasonable and fitting for the activities in which you engage (especially if conducting IBM business). If you are engaged in a virtual world primarily for IBM business purposes, we strongly encourage you to identify your avatar as affiliated with IBM. If you are engaged primarily for personal uses, consider using a different avatar.

- IBM Virtual World Guidelines

A pioneer, that IBM (IBM). A trend-setter. It was the first company to publish a code of conduct for workers enamoured of virtual environments. And soon it will be the first to create a virtual world of its own in Second Life. This morning, Big Blue announced a partnership with Second Life producer Linden Lab to create a secure, enterprise-class version of the popular Internet-based virtual world. By running a Second Life installation on servers inside IBM’s firewall, the two will homestead a sort of corporate gated community for security-conscious companies–one in which companies can conduct business without being set upon by a horde of animated flying phalli. A savvy way to drive adoption of virtual worlds in enterprise. And if all goes as planned, a host of other companies will be running Second Life inside their own firewalls by year’s end. “There has been so much hype and puffery around virtual worlds,” Ginsu Yoon, Linden’s vice president of business affairs told The Wall Street Journal. “It’s really important to Linden Lab to be able to demonstrate that it is able and willing to meet the requirements of companies like IBM.”