diff -r 000000000000 -r 6474c204b198 toolkit/devtools/server/actors/pretty-print-worker.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/devtools/server/actors/pretty-print-worker.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,53 @@
+/* -*- Mode: javascript; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; js-indent-level: 2; -*- */
+/* vim: set ft=javascript ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * This file is meant to be loaded as a ChromeWorker. It accepts messages which
+ * have data of the form:
+ *
+ *     { id, url, indent, source }
+ *
+ * Where `id` is a unique ID to identify this request, `url` is the url of the
+ * source being pretty printed, `indent` is the number of spaces to indent the
+ * code by, and `source` is the source text.
+ *
+ * On success, the worker responds with a message of the form:
+ *
+ *     { id, code, mappings }
+ *
+ * Where `id` is the same unique ID from the request, `code` is the pretty
+ * printed source text, and `mappings` is an array or source mappings from the
+ * pretty printed code back to the ugly source text.
+ *
+ * In the case of an error, the worker responds with a message of the form:
+ *
+ *     { id, error }
+ */
+
+importScripts("resource://gre/modules/devtools/acorn/acorn.js");
+importScripts("resource://gre/modules/devtools/source-map.js");
+importScripts("resource://gre/modules/devtools/pretty-fast.js");
+
+self.onmessage = (event) => {
+  const { data: { id, url, indent, source } } = event;
+  try {
+    const prettified = prettyFast(source, {
+      url: url,
+      indent: " ".repeat(indent)
+    });
+
+    self.postMessage({
+      id: id,
+      code: prettified.code,
+      mappings: prettified.map._mappings
+    });
+  } catch (e) {
+    self.postMessage({
+      id: id,
+      error: e.message + "\n" + e.stack
+    });
+  }
+};