Firecore have a new release aTV Flash the Apple TV addon for the 2nd gen Apple TV. Using Seas0nPass it enables untethered jailbreak of the Apple TV 5.3. New in version 2.4 of aTV Flash is support for the Apple TV running version 5.3, improved install process and improved diagnostic reporting.
aTV Flash adds extra functionality to the Apple TV including MKV, AVI, MP4 and WMV format support, a web browser and many other features for $29.95
Details from the Firecore blog:
Here’s more details on what’s new and how to update…
What’s new in 2.4?
•Added support for untethered Apple TV 5.3
•Improved reliability of installation process
•Improved diagnostic reporting
•Other various fixes and improvements