While Valve has been busy proving that Linux and open source are the future of gaming with the Steam operating system and gaming consoles, Mozilla and Epic Games have been making their own strides in the open source gaming revolution on the Web.

This week, Epic and Mozilla released a video preview of Epic’s Soul and Swing Ninja games running in the Firefox browser as Web applications on Epic’s forthcoming Unreal Engine 4. Using its asm.js subset of Javascript, Mozilla says it has improved gaming performance within Firefox to reach 67 percent of native speeds – up from 40 percent at last year’s demo of Unreal Engine 3. (A claim largely supported by ArsTechnica’s own testing.) And Mozilla expects it to get even faster, according to their blog post announcing the preview.

“This technology has reached a point where (the) games users can jump into via a Web link are now almost indistinguishable from (the) ones they might have had to wait to download and install,” said Brendan Eich, CTO and SVP of Engineering at Mozilla, in the blog post. “Using Emscripten to cross-compile C and C++ into asm.js, developers can run their games at near-native speeds, so they can approach the Web as they would any other platform.”