The Mozilla blog offers a trailer showing off a sneak peek of a couple of Unreal Engine 4 demos running in Firefox with no plug-ins as a glimpse at the future of web-based gaming, saying this works at near letter quality "near native speeds." Here's a bit:

Mozilla and Epic Games have showed the power of the Web as a platform for gaming by porting Unreal Engine 3 to the Web and showcasing Epic Citadel, using asm.js, a supercharged subset of JavaScript pioneered by Mozilla. In less than 12 months, optimizations have increased the performance of Web applications using asm.js from 40% to within 67% of native, and we expect it to get even faster. This performance opens up new opportunities for giving users an astonishing and delightful experience, from within their choice of Web browser. Any modern browser can run asm.js content, but specific optimizations currently present only in Firefox, ensure the most consistent and smooth experience.

“This technology has reached a point where games users can jump into via a Web link are now almost indistinguishable from ones they might have had to wait to download and install,” said Brendan Eich, CTO and SVP of Engineering at Mozilla. “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.”