Jeremy Ashkenas comments:
Please direct all thanks for this over to http://github.com/jwalton. He's been toiling away on these for a couple of months now, originally as a bit of a skunkworks. Managing to get them merged in cleanly to an oft-changing code generation codebase was no small feat.Currently, the only browsers reported to support source maps are Chrome and the WebKit Nightly Builds. (Source maps in Node.js are covered in this recent post.) To enable Source Maps in Chrome, select View -> Developer -> Developer Tools, then click on the gear icon in the lower right corner to open Settings. In the Settings dialog, check "Enable source maps" as shown below.