Go to: http://lampwww.epfl.ch/~doeraene/presentations/scala-js-scaladays2013/#/ Open debugger, and unblackbox a minified JS file. Pretty print it. When clicking the pretty print button again, the below error throws: TabSources.prototype._fetchSourceMap threw an exception: Error: Request failed with status code = 2152857618 in onStopRequest handler for url = file:///internal://sourcemap1/ Stack: fetch/streamListener.onStopRequest@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/DevToolsUtils.js:537:29 @debugger eval code:1:17 WCA_evalWithDebugger@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/actors/webconsole.js:1194:16 WCA_onEvaluateJS@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/actors/webconsole.js:806:20 WCA_onEvaluateJSAsync@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/actors/webconsole.js:777:20 DSC_onPacket@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/main.js:1469:15 ChildDebuggerTransport.prototype.receiveMessage@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/transport/transport.js:742:5 Line: 537, column: 28

This now seems to still throw the error, but seems to un pretty print ok.

The new debugger doesn't have "un-prettyprint" any more, it just has separate tabs for the prettified and unmodified sources. So, I'm closing this as "fixed".