Epic Games has ported Unreal Engine 3 over to HTML5, and it's... epic.
Epic Games announced on Thursday the launch of a version of Epic Citadel built with HTML5. This is good news for gamers, as it means Unreal Engine 3 (UE3) can be run inside a Web browser without the need for plugins, added components or a local installation on the hard drive. The only thing you'll need to experience this demo at an optimal performance is a nightly build of Mozilla's Firefox version 23 or above.
Epic Citadel also arrives with two options: a guided tour which is essentially a non-interactive demo moving the camera through various spots throughout the kingdom, and a benchmark to test the HTML5-based engine's performance on your hardware. The FAQ linked below the demo states that the framerate can be unlocked in the Firefox Nightly build by going into about:config.
Don't want to install Firefox Nightly? The FAQ also lists a few alternatives including Release Firefox which will be slower, Chrome although it crashes, and both Opera and Safari which must have WebGL activated but are currently not compatible. Internet Explorer does not support WebGL in current versions, Epic Games states.