diff -r 000000000000 -r 6474c204b198 browser/metro/base/content/contenthandlers/ConsoleAPIObserver.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/metro/base/content/contenthandlers/ConsoleAPIObserver.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,118 @@
+/* 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/. */
+
+let Ci = Components.interfaces;
+let Cc = Components.classes;
+
+dump("### ConsoleAPIObserver.js loaded\n");
+
+/*
+ * ConsoleAPIObserver
+ *
+ */ 
+
+var ConsoleAPIObserver = {
+  init: function init() {
+    addMessageListener("Browser:TabOpen", this);
+    addMessageListener("Browser:TabClose", this);
+  },
+
+  receiveMessage: function receiveMessage(aMessage) {
+    let json = aMessage.json;
+    switch (aMessage.name) {
+      case "Browser:TabOpen":
+        Services.obs.addObserver(this, "console-api-log-event", false);
+        break;
+      case "Browser:TabClose":
+        Services.obs.removeObserver(this, "console-api-log-event");
+        break;
+    }
+  },
+
+  observe: function observe(aMessage, aTopic, aData) {
+    let contentWindowId = content.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils).outerWindowID;
+    aMessage = aMessage.wrappedJSObject;
+    if (aMessage.ID != contentWindowId)
+      return;
+
+    let mappedArguments = Array.map(aMessage.arguments, this.formatResult, this);
+    let joinedArguments = Array.join(mappedArguments, " ");
+
+    if (aMessage.level == "error" || aMessage.level == "warn") {
+      let flag = (aMessage.level == "error" ? Ci.nsIScriptError.errorFlag : Ci.nsIScriptError.warningFlag);
+      let consoleMsg = Cc["@mozilla.org/scripterror;1"].createInstance(Ci.nsIScriptError);
+      consoleMsg.init(joinedArguments, null, null, 0, 0, flag, "content javascript");
+      Services.console.logMessage(consoleMsg);
+    } else if (aMessage.level == "trace") {
+      let bundle = Services.strings.createBundle("chrome://global/locale/headsUpDisplay.properties");
+      let args = aMessage.arguments;
+      let filename = this.abbreviateSourceURL(args[0].filename);
+      let functionName = args[0].functionName || bundle.GetStringFromName("stacktrace.anonymousFunction");
+      let lineNumber = args[0].lineNumber;
+
+      let body = bundle.formatStringFromName("stacktrace.outputMessage", [filename, functionName, lineNumber], 3);
+      body += "\n";
+      args.forEach(function(aFrame) {
+        body += aFrame.filename + " :: " + aFrame.functionName + " :: " + aFrame.lineNumber + "\n";
+      });
+
+      Services.console.logStringMessage(body);
+    } else {
+      Services.console.logStringMessage(joinedArguments);
+    }
+  },
+
+  getResultType: function getResultType(aResult) {
+    let type = aResult === null ? "null" : typeof aResult;
+    if (type == "object" && aResult.constructor && aResult.constructor.name)
+      type = aResult.constructor.name;
+    return type.toLowerCase();
+  },
+
+  formatResult: function formatResult(aResult) {
+    let output = "";
+    let type = this.getResultType(aResult);
+    switch (type) {
+      case "string":
+      case "boolean":
+      case "date":
+      case "error":
+      case "number":
+      case "regexp":
+        output = aResult.toString();
+        break;
+      case "null":
+      case "undefined":
+        output = type;
+        break;
+      default:
+        output = aResult.toString();
+        break;
+    }
+
+    return output;
+  },
+
+  abbreviateSourceURL: function abbreviateSourceURL(aSourceURL) {
+    // Remove any query parameters.
+    let hookIndex = aSourceURL.indexOf("?");
+    if (hookIndex > -1)
+      aSourceURL = aSourceURL.substring(0, hookIndex);
+
+    // Remove a trailing "/".
+    if (aSourceURL[aSourceURL.length - 1] == "/")
+      aSourceURL = aSourceURL.substring(0, aSourceURL.length - 1);
+
+    // Remove all but the last path component.
+    let slashIndex = aSourceURL.lastIndexOf("/");
+    if (slashIndex > -1)
+      aSourceURL = aSourceURL.substring(slashIndex + 1);
+
+    return aSourceURL;
+  }
+};
+this.ConsoleAPIObserver = ConsoleAPIObserver;
+
+ConsoleAPIObserver.init();
+