In 2011, Epic Games released a version of its Unreal Engine 3 demo, Epic Citadel, that will work with Adobe's Flash Player 11, enabling any web browser with Flash Player 11 support to run the demo. Today, Epic released a new version of the Epic Citadel demo that is designed to work in browsers that use HTML5 but that support is somewhat limited at the moment.
The Epic Citadel HTML5 webpage was developed by a joint team of Epic programmers working with a team from Mozilla, the creators of the Firefox web browser. The final result is supposed to allow anyone who uses a supported HTML5 browser to explore the medieval castle demo running on Unreal Engine 3. The demo does not have any interactive elements.
However, the FAQ page for Epic Citadel HTML5 points out that some browsers won't run the demo, even if they support HTML5. None of the versions of Microsoft's Internet Explorer will run the demo, because they don't support WebGL, which Microsoft claims is too much of a security risk to add to any version of IE. Safari and Opera also can't run Epic Citadel, even though they can support WebGL via a manual activation.
Google's Chrome web browser currently crashes when it tries to run Epic Citadel HTML5 but the FAQ page claims this problem is "expected to be resolved by the Chrome team soon." Technically, any version of Firefox should be able to run Epic Citadel HTML5, but Epic recommends that uses download the latest Firefox Nightly build for the best performance.
Source: Epic Games