diff --git a/browser/base/content/browser-menubar.inc b/browser/base/content/browser-menubar.inc
index 4947fae8a8c9..fbbabf288d2d 100644
--- a/browser/base/content/browser-menubar.inc
+++ b/browser/base/content/browser-menubar.inc
@@ -522,7 +522,7 @@
                   <menuitem id="webConsole" observes="devtoolsMenuBroadcaster_WebConsole" accesskey="&webConsoleCmd.accesskey;"/>
                   <menuitem id="menu_pageinspect" observes="devtoolsMenuBroadcaster_Inspect" accesskey="&inspectMenu.accesskey;"/>
                   <menuitem id="menu_responsiveUI" observes="devtoolsMenuBroadcaster_ResponsiveUI" accesskey="&responsiveDesignTool.accesskey;"/>
-                  <menuitem id="menu_debugger" observes="devtoolsMenuBroadcaster_Debugger"/>
+                  <menuitem id="menu_debugger" observes="devtoolsMenuBroadcaster_Debugger" accesskey="&debuggerMenu.accesskey;"/>
                   <menuitem id="menu_remoteDebugger" observes="devtoolsMenuBroadcaster_RemoteDebugger"/>
                   <menuitem id="menu_chromeDebugger" observes="devtoolsMenuBroadcaster_ChromeDebugger"/>
                   <menuitem id="menu_scratchpad" observes="devtoolsMenuBroadcaster_Scratchpad" accesskey="&scratchpad.accesskey;"/>
diff --git a/browser/devtools/commandline/CmdDbg.jsm b/browser/devtools/commandline/CmdDbg.jsm
index c74cbf9578e4..f30593598580 100644
--- a/browser/devtools/commandline/CmdDbg.jsm
+++ b/browser/devtools/commandline/CmdDbg.jsm
@@ -18,6 +18,47 @@ gcli.addCommand({
   manual: gcli.lookup("dbgManual")
 });
 
+/**
+ * 'dbg open' command
+ */
+gcli.addCommand({
+  name: "dbg open",
+  description: gcli.lookup("dbgOpen"),
+  params: [],
+  exec: function (args, context) {
+    let win = context.environment.chromeDocument.defaultView;
+    let tab = win.gBrowser.selectedTab;
+    let dbg = win.DebuggerUI.findDebugger();
+
+    if (dbg) {
+      if (dbg.ownerTab !== tab) {
+        win.DebuggerUI.toggleDebugger();
+      }
+
+      return;
+    }
+
+    win.DebuggerUI.toggleDebugger();
+  }
+});
+
+/**
+ * 'dbg close' command
+ */
+gcli.addCommand({
+  name: "dbg close",
+  description: gcli.lookup("dbgClose"),
+  params: [],
+  exec: function (args, context) {
+    let win = context.environment.chromeDocument.defaultView;
+    let tab = win.gBrowser.selectedTab;
+    let dbg = win.DebuggerUI.findDebugger();
+
+    if (dbg) {
+      dbg.close();
+    }
+  }
+});
 
 /**
  * 'dbg interrupt' command
diff --git a/browser/devtools/commandline/test/browser_dbg_cmd.js b/browser/devtools/commandline/test/browser_dbg_cmd.js
index eef119a5cb29..8011c8c9fa2f 100644
--- a/browser/devtools/commandline/test/browser_dbg_cmd.js
+++ b/browser/devtools/commandline/test/browser_dbg_cmd.js
@@ -8,8 +8,13 @@ function test() {
 }
 
 function testDbgCmd() {
-  let pane = DebuggerUI.toggleDebugger();
-  ok(pane, "toggleDebugger() should return a pane.");
+  DeveloperToolbarTest.exec({
+    typed: "dbg open",
+    blankOutput: true
+  });
+
+  let pane = DebuggerUI.findDebugger();
+  ok(pane, "Debugger was opened.");
   let frame = pane._frame;
 
   frame.addEventListener("Debugger:Connecting", function dbgConnected(aEvent) {
@@ -41,9 +46,14 @@ function testDbgCmd() {
                       cmd("dbg continue", function() {
                         cmd("dbg continue", function() {
                           is(output.value, "dbg continue", "debugger continued");
-                          pane.contentWindow.gClient.close(function() {
-                            finish();
+                          DeveloperToolbarTest.exec({
+                            typed: "dbg close",
+                            blankOutput: true
                           });
+
+                          let dbg = DebuggerUI.findDebugger();
+                          ok(!dbg, "Debugger was closed.");
+                          finish();
                         });
                       });
                     });
diff --git a/browser/devtools/debugger/debugger-controller.js b/browser/devtools/debugger/debugger-controller.js
index f7e5a545bb42..57d770deb6ae 100644
--- a/browser/devtools/debugger/debugger-controller.js
+++ b/browser/devtools/debugger/debugger-controller.js
@@ -9,6 +9,7 @@ const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cu = Components.utils;
 
+const NEW_SCRIPT_DISPLAY_DELAY = 100; // ms
 const FRAME_STEP_CACHE_DURATION = 100; // ms
 const DBG_STRINGS_URI = "chrome://browser/locale/devtools/debugger.properties";
 const SCRIPTS_URL_MAX_LENGTH = 64; // chars
@@ -929,7 +930,11 @@ SourceScripts.prototype = {
       return;
     }
 
-    this._addScript({ url: aPacket.url, startLine: aPacket.startLine }, true);
+    this._addScript({
+      url: aPacket.url,
+      startLine: aPacket.startLine,
+      source: aPacket.source
+    }, true);
 
     let preferredScriptUrl = DebuggerView.Scripts.preferredScriptUrl;
 
@@ -937,15 +942,21 @@ SourceScripts.prototype = {
     if (aPacket.url === DebuggerView.Scripts.preferredScriptUrl) {
       DebuggerView.Scripts.selectScript(aPacket.url);
     }
-    // ..or the first entry if there's not one selected yet.
-    else if (!DebuggerView.Scripts.selected) {
-      DebuggerView.Scripts.selectIndex(0);
-      // Selecting a script would make it "preferred", which is a lie here,
-      // because we're only displaying a script to make sure there's always
-      // something available in the SourceEditor and the scripts menulist.
-      // Hence the need revert back to the initial preferred script, just
-      // in case it will be available soon.
-      DebuggerView.Scripts.preferredScriptUrl = preferredScriptUrl;
+    // ..or the first entry if there's none selected yet after a while
+    else {
+      window.setTimeout(function() {
+        // If after a certain delay the preferred script still wasn't received,
+        // just give up on waiting and display the first entry.
+        if (!DebuggerView.Scripts.selected) {
+          DebuggerView.Scripts.selectIndex(0);
+          // Selecting a script would make it "preferred", which is a lie here,
+          // because we're only displaying a script to make sure there's always
+          // something available in the SourceEditor and the scripts menulist.
+          // Hence the need revert back to the initial preferred script, just
+          // in case it will be available soon.
+          DebuggerView.Scripts.preferredScriptUrl = preferredScriptUrl;
+        }
+      }, NEW_SCRIPT_DISPLAY_DELAY);
     }
 
     // If there are any stored breakpoints for this script, display them again,
@@ -1206,7 +1217,11 @@ SourceScripts.prototype = {
    */
   showScript: function SS_showScript(aScript, aOptions = {}) {
     if (aScript.loaded) {
-      this._onShowScript(aScript, aOptions);
+      // Scripts may take a longer time to load than expected, therefore the
+      // required one may change at any time after a previous request was made.
+      if (aScript.url === DebuggerView.Scripts.selected) {
+        this._onShowScript(aScript, aOptions);
+      }
       return;
     }
 
@@ -1217,7 +1232,7 @@ SourceScripts.prototype = {
 
     // Notify that we need to load a script file.
     DebuggerController.dispatchEvent("Debugger:LoadSource", {
-      url: aScript.url,
+      script: aScript,
       options: aOptions
     });
   },
@@ -1256,84 +1271,22 @@ SourceScripts.prototype = {
   },
 
   /**
-   * Handles notifications to load a source script from the cache or from a
-   * local file.
-   *
-   * XXX: It may be better to use nsITraceableChannel to get to the sources
-   * without relying on caching when we can (not for eval, etc.):
-   * http://www.softwareishard.com/blog/firebug/nsitraceablechannel-intercept-http-traffic/
+   * Handles notifications to load a source script.
    */
   _onLoadSource: function SS__onLoadSource(aEvent) {
-    let url = aEvent.detail.url;
+    let script = aEvent.detail.script;
     let options = aEvent.detail.options;
-    let self = this;
 
-    switch (Services.io.extractScheme(url)) {
-      case "file":
-      case "chrome":
-      case "resource":
-        try {
-          NetUtil.asyncFetch(url, function onFetch(aStream, aStatus) {
-            if (!Components.isSuccessCode(aStatus)) {
-              return self._logError(url, aStatus);
-            }
-            let source = NetUtil.readInputStreamToString(aStream, aStream.available());
-            source = self._convertToUnicode(source);
-            self._onLoadSourceFinished(url, source, null, options);
-            aStream.close();
-          });
-        } catch (ex) {
-          return self._logError(url, ex.name);
-        }
-        break;
+    let sourceClient = this.activeThread.source(script.source);
+    sourceClient.source(function (aResponse) {
+      if (aResponse.error) {
+        return this._logError(script.url, -1);
+      }
 
-      default:
-        let channel = Services.io.newChannel(url, null, null);
-        let chunks = [];
-        let streamListener = {
-          onStartRequest: function(aRequest, aContext, aStatusCode) {
-            if (!Components.isSuccessCode(aStatusCode)) {
-              return self._logError(url, aStatusCode);
-            }
-          },
-          onDataAvailable: function(aRequest, aContext, aStream, aOffset, aCount) {
-            chunks.push(NetUtil.readInputStreamToString(aStream, aCount));
-          },
-          onStopRequest: function(aRequest, aContext, aStatusCode) {
-            if (!Components.isSuccessCode(aStatusCode)) {
-              return self._logError(url, aStatusCode);
-            }
-            let source = self._convertToUnicode(chunks.join(""), channel.contentCharset);
-            self._onLoadSourceFinished(url, source, channel.contentType, options);
-          }
-        };
-
-        channel.loadFlags = channel.LOAD_FROM_CACHE;
-        channel.asyncOpen(streamListener, null);
-        break;
-    }
-  },
-
-  /**
-   * Convert a given string, encoded in a given character set, to unicode.
-   * @param string aString
-   *        A string.
-   * @param string aCharset
-   *        A character set.
-   * @return string
-   *         A unicode string.
-   */
-  _convertToUnicode: function SS__convertToUnicode(aString, aCharset) {
-    // Decoding primitives.
-    let converter = Cc["@mozilla.org/intl/scriptableunicodeconverter"]
-        .createInstance(Ci.nsIScriptableUnicodeConverter);
-
-    try {
-      converter.charset = aCharset || "UTF-8";
-      return converter.ConvertToUnicode(aString);
-    } catch(e) {
-      return aString;
-    }
+      this._onLoadSourceFinished(script.url,
+                                 aResponse.source,
+                                 options);
+    }.bind(this));
   },
 
   /**
@@ -1344,14 +1297,12 @@ SourceScripts.prototype = {
    *        The URL of the source script.
    * @param string aSourceText
    *        The text of the source script.
-   * @param string aContentType
-   *        The content type of the source script.
    * @param object aOptions [optional]
    *        Additional options for showing the script. Supported options:
    *        - targetLine: place the editor at the given line number.
    */
   _onLoadSourceFinished:
-  function SS__onLoadSourceFinished(aScriptUrl, aSourceText, aContentType, aOptions) {
+  function SS__onLoadSourceFinished(aScriptUrl, aSourceText, aOptions) {
     let element = DebuggerView.Scripts.getScriptByLocation(aScriptUrl);
 
     // Tab navigated before we got a chance to finish loading and displaying
@@ -1367,7 +1318,6 @@ SourceScripts.prototype = {
 
     script.loaded = true;
     script.text = aSourceText;
-    script.contentType = aContentType;
     element.setUserData("sourceScript", script, null);
 
     if (aOptions.silent) {
diff --git a/browser/devtools/debugger/debugger-view.js b/browser/devtools/debugger/debugger-view.js
index 79b254be1217..4e9a9613bb9e 100644
--- a/browser/devtools/debugger/debugger-view.js
+++ b/browser/devtools/debugger/debugger-view.js
@@ -468,7 +468,7 @@ GlobalSearchView.prototype = {
         continue;
       }
       DebuggerController.dispatchEvent("Debugger:LoadSource", {
-        url: url,
+        script: DebuggerView.Scripts.getScriptByLocation(url).getUserData("sourceScript"),
         options: {
           silent: true,
           callback: aFetchCallback
diff --git a/browser/devtools/debugger/test/browser_dbg_location-changes-new.js b/browser/devtools/debugger/test/browser_dbg_location-changes-new.js
index 28040421b4b4..d5dbc9575aa0 100644
--- a/browser/devtools/debugger/test/browser_dbg_location-changes-new.js
+++ b/browser/devtools/debugger/test/browser_dbg_location-changes-new.js
@@ -59,7 +59,7 @@ function testLocationChange()
       ok(true, "tabNavigated event was fired.");
       info("Still attached to the tab.");
 
-      gDebugger.addEventListener("Debugger:AfterNewScript", function _onEvent(aEvent) {
+      gDebugger.addEventListener("Debugger:ScriptShown", function _onEvent(aEvent) {
         gDebugger.removeEventListener(aEvent.type, _onEvent);
 
         isnot(gDebugger.DebuggerView.Scripts.selected, null,
diff --git a/browser/devtools/debugger/test/browser_dbg_reload-same-script.js b/browser/devtools/debugger/test/browser_dbg_reload-same-script.js
index bc23e6ff0b15..5b4673d0b1d9 100644
--- a/browser/devtools/debugger/test/browser_dbg_reload-same-script.js
+++ b/browser/devtools/debugger/test/browser_dbg_reload-same-script.js
@@ -170,18 +170,24 @@ function test()
   {
     let scriptsView = gView.Scripts;
     let scriptLocations = scriptsView.scriptLocations;
-    info("Available scripts: " + scriptLocations);
 
-    if (scriptLocations.length === 2) {
+    // Poll every few milliseconds until the scripts are retrieved.
+    let count = 0;
+    let intervalID = window.setInterval(function() {
+      dump("count: " + count + " ");
+      if (++count > 50) {
+        ok(false, "Timed out while polling for the scripts.");
+        closeDebuggerAndFinish();
+      }
+      if (scriptLocations.length !== 2) {
+        return;
+      }
+      info("Available scripts: " + scriptLocations);
+
       // We got all the scripts, it's safe to switch.
+      window.clearInterval(intervalID);
       scriptsView.selectScript(scriptLocations[index]);
-      return;
-    }
-
-    window.addEventListener("Debugger:AfterNewScript", function _onEvent(aEvent) {
-      window.removeEventListener(aEvent.type, _onEvent);
-      switchScript(index);
-    });
+    }, 100);
   }
 
   function reloadPage()
diff --git a/browser/devtools/markupview/markup-view.xhtml b/browser/devtools/markupview/markup-view.xhtml
index 3d0893add337..191655ec4c70 100644
--- a/browser/devtools/markupview/markup-view.xhtml
+++ b/browser/devtools/markupview/markup-view.xhtml
@@ -11,7 +11,7 @@
   <link rel="stylesheet" href="chrome://browser/skin/devtools/markup-view.css" type="text/css"/>
   <link rel="stylesheet" href="chrome://browser/skin/devtools/common.css" type="text/css"/>
 </head>
-<body role="application">
+<body class="devtools-theme-background" role="application">
   <div id="root"></div>
   <div id="templates" style="display:none">
     <ul>
diff --git a/browser/devtools/responsivedesign/responsivedesign.jsm b/browser/devtools/responsivedesign/responsivedesign.jsm
index d6b0db95ae42..c43a071594e4 100644
--- a/browser/devtools/responsivedesign/responsivedesign.jsm
+++ b/browser/devtools/responsivedesign/responsivedesign.jsm
@@ -9,6 +9,7 @@ const Cu = Components.utils;
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource:///modules/devtools/FloatingScrollbars.jsm");
 
 var EXPORTED_SYMBOLS = ["ResponsiveUIManager"];
 
@@ -159,6 +160,8 @@ function ResponsiveUI(aWindow, aTab)
       this.rotate();
     }
   } catch(e) {}
+
+  switchToFloatingScrollbars(this.tab);
 }
 
 ResponsiveUI.prototype = {
@@ -179,6 +182,7 @@ ResponsiveUI.prototype = {
   close: function RUI_unload() {
     if (this.closing)
       return;
+    switchToNativeScrollbars(this.tab);
     this.closing = true;
 
     this.unCheckMenus();
diff --git a/browser/devtools/responsivedesign/test/browser_responsiveui.js b/browser/devtools/responsivedesign/test/browser_responsiveui.js
index 54729bfcf548..071f32d34bb8 100644
--- a/browser/devtools/responsivedesign/test/browser_responsiveui.js
+++ b/browser/devtools/responsivedesign/test/browser_responsiveui.js
@@ -31,11 +31,27 @@ function test() {
     instance = gBrowser.selectedTab.__responsiveUI;
     ok(instance, "instance of the module is attached to the tab.");
 
+    ensureScrollbarsAreFloating();
+
     instance.transitionsEnabled = false;
 
     testPresets();
   }
 
+  function ensureScrollbarsAreFloating() {
+    let body = gBrowser.contentDocument.body;
+    let html = gBrowser.contentDocument.documentElement;
+
+    let originalWidth = body.getBoundingClientRect().width;
+
+    html.style.overflowY = "scroll"; // Force scrollbars
+    // Flush. Should not be needed as getBoundingClientRect() should flush,
+    // but just in case.
+    gBrowser.contentWindow.getComputedStyle(html).overflowY;
+    let newWidth = body.getBoundingClientRect().width;
+    is(originalWidth, newWidth, "Floating scrollbars are presents");
+  }
+
   function testPresets() {
     function testOnePreset(c) {
       if (c == 0) {
diff --git a/browser/devtools/shared/DeveloperToolbar.jsm b/browser/devtools/shared/DeveloperToolbar.jsm
index a4606f3bb02a..7873890a28ae 100644
--- a/browser/devtools/shared/DeveloperToolbar.jsm
+++ b/browser/devtools/shared/DeveloperToolbar.jsm
@@ -765,7 +765,7 @@ OutputPanel.prototype.remove = function OP_remove()
     this.canHide = true;
   }
 
-  if (this._panel) {
+  if (this._panel && this._panel.hidePopup) {
     this._panel.hidePopup();
   }
 
@@ -992,7 +992,9 @@ TooltipPanel.prototype.remove = function TP_remove()
   if (isLinux) {
     this.canHide = true;
   }
-  this._panel.hidePopup();
+  if (this._panel && this._panel.hidePopup) {
+    this._panel.hidePopup();
+  }
 };
 
 /**
diff --git a/browser/devtools/shared/FloatingScrollbars.jsm b/browser/devtools/shared/FloatingScrollbars.jsm
new file mode 100644
index 000000000000..3ed738c88f34
--- /dev/null
+++ b/browser/devtools/shared/FloatingScrollbars.jsm
@@ -0,0 +1,126 @@
+/* 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/. */
+
+"use strict";
+
+const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
+
+const EXPORTED_SYMBOLS = [ "switchToFloatingScrollbars", "switchToNativeScrollbars" ];
+
+Cu.import("resource://gre/modules/Services.jsm");
+
+let URL = Services.io.newURI("chrome://browser/skin/devtools/floating-scrollbars.css", null, null);
+
+let trackedTabs = new WeakMap();
+
+/**
+ * Switch to floating scrollbars, à la mobile.
+ *
+ * @param aTab the targeted tab.
+ *
+ */
+function switchToFloatingScrollbars(aTab) {
+  let mgr = trackedTabs.get(aTab);
+  if (!mgr) {
+    mgr = new ScrollbarManager(aTab);
+  }
+  mgr.switchToFloating();
+}
+
+/**
+ * Switch to original native scrollbars.
+ *
+ * @param aTab the targeted tab.
+ *
+ */
+function switchToNativeScrollbars(aTab) {
+  let mgr = trackedTabs.get(aTab);
+  if (mgr) {
+    mgr.reset();
+  }
+}
+
+function ScrollbarManager(aTab) {
+  trackedTabs.set(aTab, this);
+
+  this.attachedTab = aTab;
+  this.attachedBrowser = aTab.linkedBrowser;
+
+  this.reset = this.reset.bind(this);
+  this.switchToFloating = this.switchToFloating.bind(this);
+
+  this.attachedTab.addEventListener("TabClose", this.reset, true);
+  this.attachedBrowser.addEventListener("DOMContentLoaded", this.switchToFloating, true);
+}
+
+ScrollbarManager.prototype = {
+  get win() {
+    return this.attachedBrowser.contentWindow;
+  },
+
+  /*
+   * Change the look of the scrollbars.
+   */
+  switchToFloating: function() {
+    let windows = this.getInnerWindows(this.win);
+    windows.forEach(this.injectStyleSheet);
+    this.forceStyle();
+  },
+
+
+  /*
+   * Reset the look of the scrollbars.
+   */
+  reset: function() {
+    let windows = this.getInnerWindows(this.win);
+    windows.forEach(this.removeStyleSheet);
+    this.forceStyle(this.attachedBrowser);
+    this.attachedBrowser.removeEventListener("DOMContentLoaded", this.switchToFloating, true);
+    this.attachedTab.removeEventListener("TabClose", this.reset, true);
+    trackedTabs.delete(this.attachedTab);
+  },
+
+  /*
+   * Toggle the display property of the window to force the style to be applied.
+   */
+  forceStyle: function() {
+    let parentWindow = this.attachedBrowser.ownerDocument.defaultView;
+    let display = parentWindow.getComputedStyle(this.attachedBrowser).display; // Save display value
+    this.attachedBrowser.style.display = "none";
+    parentWindow.getComputedStyle(this.attachedBrowser).display; // Flush
+    this.attachedBrowser.style.display = display; // Restore
+  },
+
+  /*
+   * return all the window objects present in the hiearchy of a window.
+   */
+  getInnerWindows: function(win) {
+    let iframes = win.document.querySelectorAll("iframe");
+    let innerWindows = [];
+    for (let iframe of iframes) {
+      innerWindows = innerWindows.concat(this.getInnerWindows(iframe.contentWindow));
+    }
+    return [win].concat(innerWindows);
+  },
+
+  /*
+   * Append the new scrollbar style.
+   */
+  injectStyleSheet: function(win) {
+    let winUtils = win.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+    try {
+      winUtils.loadSheet(URL, win.AGENT_SHEET);
+    }catch(e) {}
+  },
+
+  /*
+   * Remove the injected stylesheet.
+   */
+  removeStyleSheet: function(win) {
+    let winUtils = win.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+    try {
+      winUtils.removeSheet(URL, win.AGENT_SHEET);
+    }catch(e) {}
+  },
+}
diff --git a/browser/devtools/shared/test/browser_promise_basic.js b/browser/devtools/shared/test/browser_promise_basic.js
index 9e78c8426c0a..2466e4982810 100644
--- a/browser/devtools/shared/test/browser_promise_basic.js
+++ b/browser/devtools/shared/test/browser_promise_basic.js
@@ -4,7 +4,7 @@
 // Tests that our Promise implementation works properly
 
 let tempScope = {};
-Cu.import("resource:///modules/devtools/Promise.jsm", tempScope);
+Cu.import("resource://gre/modules/devtools/_Promise.jsm", tempScope);
 let Promise = tempScope.Promise;
 
 function test() {
diff --git a/browser/devtools/shared/test/browser_templater_basic.js b/browser/devtools/shared/test/browser_templater_basic.js
index 376daee2215b..6d83220f379d 100644
--- a/browser/devtools/shared/test/browser_templater_basic.js
+++ b/browser/devtools/shared/test/browser_templater_basic.js
@@ -11,7 +11,7 @@
 
 var imports = {};
 Cu.import("resource:///modules/devtools/Templater.jsm", imports);
-Cu.import("resource:///modules/devtools/Promise.jsm", imports);
+Cu.import("resource://gre/modules/devtools/_Promise.jsm", imports);
 
 function test() {
   addTab("http://example.com/browser/browser/devtools/shared/test/browser_templater_basic.html", function() {
diff --git a/browser/devtools/styleinspector/CssRuleView.jsm b/browser/devtools/styleinspector/CssRuleView.jsm
index 296837b267bf..df0a9139bb3a 100644
--- a/browser/devtools/styleinspector/CssRuleView.jsm
+++ b/browser/devtools/styleinspector/CssRuleView.jsm
@@ -1629,13 +1629,6 @@ TextPropertyEditor.prototype = {
       tabindex: "0",
     });
 
-    editableField({
-      start: this._onStartEditing,
-      element: this.valueSpan,
-      done: this._onValueDone,
-      advanceChars: ';'
-    });
-
     // Save the initial value as the last committed value,
     // for restoring after pressing escape.
     this.committed = { name: this.prop.name,
@@ -1655,6 +1648,15 @@ TextPropertyEditor.prototype = {
     this.computed = createChild(this.element, "ul", {
       class: "ruleview-computedlist",
     });
+
+    editableField({
+      start: this._onStartEditing,
+      element: this.valueSpan,
+      done: this._onValueDone,
+      validate: this._validate.bind(this),
+      warning: this.warning,
+      advanceChars: ';'
+    });
   },
 
   /**
@@ -1841,17 +1843,30 @@ TextPropertyEditor.prototype = {
   /**
    * Validate this property.
    *
+   * @param {String} [aValue]
+   *        Override the actual property value used for validation without
+   *        applying property values e.g. validate as you type.
+   *
    * @returns {Boolean}
    *          True if the property value is valid, false otherwise.
    */
-  _validate: function TextPropertyEditor_validate()
+  _validate: function TextPropertyEditor_validate(aValue)
   {
     let name = this.prop.name;
-    let value = this.prop.value;
+    let value = typeof aValue == "undefined" ? this.prop.value : aValue;
+    let val = this._parseValue(value);
     let style = this.doc.createElementNS(HTML_NS, "div").style;
+    let prefs = Services.prefs;
 
-    style.setProperty(name, value, null);
+    // We toggle output of errors whilst the user is typing a property value.
+    let prefVal = Services.prefs.getBoolPref("layout.css.report_errors");
+    prefs.setBoolPref("layout.css.report_errors", false);
 
+    try {
+      style.setProperty(name, val.value, val.priority);
+    } finally {
+      prefs.setBoolPref("layout.css.report_errors", prefVal);
+    }
     return !!style.getPropertyValue(name);
   },
 };
@@ -1971,6 +1986,7 @@ function InplaceEditor(aOptions, aEvent)
   this._onBlur = this._onBlur.bind(this);
   this._onKeyPress = this._onKeyPress.bind(this);
   this._onInput = this._onInput.bind(this);
+  this._onKeyup = this._onKeyup.bind(this);
 
   this._createInput();
   this._autosize();
@@ -1998,6 +2014,13 @@ function InplaceEditor(aOptions, aEvent)
   this.input.addEventListener("input", this._onInput, false);
   this.input.addEventListener("mousedown", function(aEvt) { aEvt.stopPropagation(); }, false);
 
+  this.warning = aOptions.warning;
+  this.validate = aOptions.validate;
+
+  if (this.warning && this.validate) {
+    this.input.addEventListener("keyup", this._onKeyup, false);
+  }
+
   if (aOptions.start) {
     aOptions.start(this, aEvent);
   }
@@ -2026,6 +2049,7 @@ InplaceEditor.prototype = {
 
     this.input.removeEventListener("blur", this._onBlur, false);
     this.input.removeEventListener("keypress", this._onKeyPress, false);
+    this.input.removeEventListener("keyup", this._onKeyup, false);
     this.input.removeEventListener("oninput", this._onInput, false);
     this._stopAutosize();
 
@@ -2128,10 +2152,12 @@ InplaceEditor.prototype = {
   /**
    * Handle loss of focus by calling done if it hasn't been called yet.
    */
-  _onBlur: function InplaceEditor_onBlur(aEvent)
+  _onBlur: function InplaceEditor_onBlur(aEvent, aDoNotClear)
   {
     this._apply();
-    this._clear();
+    if (!aDoNotClear) {
+      this._clear();
+    }
   },
 
   _onKeyPress: function InplaceEditor_onKeyPress(aEvent)
@@ -2193,11 +2219,26 @@ InplaceEditor.prototype = {
     }
   },
 
+  /**
+   * Handle the input field's keyup event.
+   */
+  _onKeyup: function(aEvent) {
+    // Validate the entered value.
+    this.warning.hidden = this.validate(this.input.value);
+    this._applied = false;
+    this._onBlur(null, true);
+  },
+
   /**
    * Handle changes the input text.
    */
   _onInput: function InplaceEditor_onInput(aEvent)
   {
+    // Validate the entered value.
+    if (this.warning && this.validate) {
+      this.warning.hidden = this.validate(this.input.value);
+    }
+
     // Update size if we're autosizing.
     if (this._measurement) {
       this._updateSize();
diff --git a/browser/devtools/styleinspector/test/browser_ruleview_ui.js b/browser/devtools/styleinspector/test/browser_ruleview_ui.js
index 89a8f09e56c6..f6e39d90eb13 100644
--- a/browser/devtools/styleinspector/test/browser_ruleview_ui.js
+++ b/browser/devtools/styleinspector/test/browser_ruleview_ui.js
@@ -170,6 +170,8 @@ function testEditProperty()
 
       for each (let ch in "red;") {
         EventUtils.sendChar(ch, ruleDialog);
+        is(propEditor.warning.hidden, ch == "d" || ch == ";",
+          "warning triangle is hidden or shown as appropriate");
       }
     });
     for each (let ch in "border-color:") {
@@ -201,7 +203,6 @@ function testDisableProperty()
 
 function finishTest()
 {
-  ruleView.element.removeEventListener("CssRuleViewChanged", ruleViewChanged, false);
   ruleView.clear();
   ruleDialog.close();
   ruleDialog = ruleView = null;
diff --git a/browser/locales/en-US/chrome/browser/devtools/debugger.dtd b/browser/locales/en-US/chrome/browser/devtools/debugger.dtd
index cda44218d6f0..d88efe3d0232 100644
--- a/browser/locales/en-US/chrome/browser/devtools/debugger.dtd
+++ b/browser/locales/en-US/chrome/browser/devtools/debugger.dtd
@@ -15,6 +15,10 @@
   -  application menu item that opens the debugger UI. -->
 <!ENTITY debuggerMenu.label2            "Debugger">
 
+<!-- LOCALIZATION NOTE (debuggerMenu.accesskey): This is accesskey for the
+  -  Tools meny entry of Debugger that opens the debugger UI. -->
+<!ENTITY debuggerMenu.accesskey         "D">
+
 <!-- LOCALIZATION NOTE (remoteDebuggerMenu.label): This is the label for the
   -  application menu item that opens the remote debugger UI. -->
 <!ENTITY remoteDebuggerMenu.label       "Remote Debugger">
diff --git a/browser/locales/en-US/chrome/browser/devtools/gclicommands.properties b/browser/locales/en-US/chrome/browser/devtools/gclicommands.properties
index 8983e4d2741e..18ec2afd9794 100644
--- a/browser/locales/en-US/chrome/browser/devtools/gclicommands.properties
+++ b/browser/locales/en-US/chrome/browser/devtools/gclicommands.properties
@@ -380,6 +380,14 @@ dbgDesc=Manage debugger
 # set of commands that control the debugger.
 dbgManual=Commands to interrupt or resume the main thread, step in, out and over lines of code
 
+# LOCALIZATION NOTE (dbgOpen) A very short string used to describe the function
+# of the dbg open command.
+dbgOpen=Open the debugger
+
+# LOCALIZATION NOTE (dbgClose) A very short string used to describe the function
+# of the dbg close command.
+dbgClose=Close the debugger
+
 # LOCALIZATION NOTE (dbgInterrupt) A very short string used to describe the
 # function of the dbg interrupt command.
 dbgInterrupt=Pauses the main thread
diff --git a/browser/themes/gnomestripe/devtools/floating-scrollbars.css b/browser/themes/gnomestripe/devtools/floating-scrollbars.css
new file mode 100644
index 000000000000..e27de04dedca
--- /dev/null
+++ b/browser/themes/gnomestripe/devtools/floating-scrollbars.css
@@ -0,0 +1,33 @@
+@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
+
+scrollbar {
+  -moz-appearance: none !important;
+  position: relative;
+  background-color: transparent;
+  background-image: none;
+  z-index: 2147483647;
+  padding: 2px;
+}
+
+scrollbar[orient="vertical"] {
+  -moz-margin-start: -8px;
+  min-width: 8px;
+  max-width: 8px;
+}
+
+scrollbar[orient="horizontal"] {
+  margin-top: -8px;
+  min-height: 8px;
+  max-height: 8px;
+}
+
+scrollbar thumb {
+  -moz-appearance: none !important;
+  border-width: 0px !important;
+  background-color: rgba(0,0,0,0.2) !important;
+  border-radius: 3px !important;
+}
+
+scrollbar scrollbarbutton, scrollbar gripper {
+  display: none;
+}
diff --git a/browser/themes/gnomestripe/jar.mn b/browser/themes/gnomestripe/jar.mn
index 5402fd59e92a..df1daa3c2be5 100644
--- a/browser/themes/gnomestripe/jar.mn
+++ b/browser/themes/gnomestripe/jar.mn
@@ -165,6 +165,7 @@ browser.jar:
   skin/classic/browser/devtools/responsive-vertical-resizer.png (devtools/responsive-vertical-resizer.png)
   skin/classic/browser/devtools/responsive-background.png (devtools/responsive-background.png)
   skin/classic/browser/devtools/tools-icons-small.png     (devtools/tools-icons-small.png)
+  skin/classic/browser/devtools/floating-scrollbars.css   (devtools/floating-scrollbars.css)
 #ifdef MOZ_SERVICES_SYNC
   skin/classic/browser/sync-16-throbber.png
   skin/classic/browser/sync-16.png
diff --git a/browser/themes/pinstripe/devtools/floating-scrollbars.css b/browser/themes/pinstripe/devtools/floating-scrollbars.css
new file mode 100644
index 000000000000..25e6d29de030
--- /dev/null
+++ b/browser/themes/pinstripe/devtools/floating-scrollbars.css
@@ -0,0 +1,30 @@
+@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
+
+scrollbar {
+  -moz-appearance: none;
+  position: relative;
+  background-color: transparent;
+  background-image: none;
+  border: 0px solid transparent;
+  z-index: 2147483647;
+  -moz-box-align: start;
+  padding: 2px;
+}
+
+scrollbar[orient="vertical"] {
+  -moz-margin-start: -8px;
+  min-width: 8px;
+  max-width: 8px;
+}
+
+scrollbar[orient="horizontal"] {
+  margin-top: -8px;
+  min-height: 8px;
+  max-height: 8px;
+}
+
+thumb {
+  -moz-appearance: none !important;
+  background-color: rgba(0,0,0,0.2);
+  border-radius: 3px;
+}
diff --git a/browser/themes/pinstripe/jar.mn b/browser/themes/pinstripe/jar.mn
index aa30f1336d98..1fff34f6ee05 100644
--- a/browser/themes/pinstripe/jar.mn
+++ b/browser/themes/pinstripe/jar.mn
@@ -235,6 +235,7 @@ browser.jar:
   skin/classic/browser/devtools/responsive-vertical-resizer.png (devtools/responsive-vertical-resizer.png)
   skin/classic/browser/devtools/responsive-background.png   (devtools/responsive-background.png)
   skin/classic/browser/devtools/tools-icons-small.png       (devtools/tools-icons-small.png)
+  skin/classic/browser/devtools/floating-scrollbars.css     (devtools/floating-scrollbars.css)
 #ifdef MOZ_SERVICES_SYNC
   skin/classic/browser/sync-throbber.png
   skin/classic/browser/sync-16.png
diff --git a/browser/themes/winstripe/devtools/floating-scrollbars.css b/browser/themes/winstripe/devtools/floating-scrollbars.css
new file mode 100644
index 000000000000..e27de04dedca
--- /dev/null
+++ b/browser/themes/winstripe/devtools/floating-scrollbars.css
@@ -0,0 +1,33 @@
+@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
+
+scrollbar {
+  -moz-appearance: none !important;
+  position: relative;
+  background-color: transparent;
+  background-image: none;
+  z-index: 2147483647;
+  padding: 2px;
+}
+
+scrollbar[orient="vertical"] {
+  -moz-margin-start: -8px;
+  min-width: 8px;
+  max-width: 8px;
+}
+
+scrollbar[orient="horizontal"] {
+  margin-top: -8px;
+  min-height: 8px;
+  max-height: 8px;
+}
+
+scrollbar thumb {
+  -moz-appearance: none !important;
+  border-width: 0px !important;
+  background-color: rgba(0,0,0,0.2) !important;
+  border-radius: 3px !important;
+}
+
+scrollbar scrollbarbutton, scrollbar gripper {
+  display: none;
+}
diff --git a/browser/themes/winstripe/jar.mn b/browser/themes/winstripe/jar.mn
index 603c039aeb47..a82b5cfae819 100644
--- a/browser/themes/winstripe/jar.mn
+++ b/browser/themes/winstripe/jar.mn
@@ -192,6 +192,7 @@ browser.jar:
         skin/classic/browser/devtools/responsive-vertical-resizer.png (devtools/responsive-vertical-resizer.png)
         skin/classic/browser/devtools/responsive-background.png     (devtools/responsive-background.png)
         skin/classic/browser/devtools/tools-icons-small.png         (devtools/tools-icons-small.png)
+        skin/classic/browser/devtools/floating-scrollbars.css       (devtools/floating-scrollbars.css)
 #ifdef MOZ_SERVICES_SYNC
         skin/classic/browser/sync-throbber.png
         skin/classic/browser/sync-16.png
@@ -395,6 +396,7 @@ browser.jar:
         skin/classic/aero/browser/devtools/responsive-vertical-resizer.png (devtools/responsive-vertical-resizer.png)
         skin/classic/aero/browser/devtools/responsive-background.png (devtools/responsive-background.png)
         skin/classic/aero/browser/devtools/tools-icons-small.png     (devtools/tools-icons-small.png)
+        skin/classic/aero/browser/devtools/floating-scrollbars.css   (devtools/floating-scrollbars.css)
 #ifdef MOZ_SERVICES_SYNC
         skin/classic/aero/browser/sync-throbber.png
         skin/classic/aero/browser/sync-16.png
diff --git a/browser/devtools/shared/Promise.jsm b/toolkit/devtools/_Promise.jsm
similarity index 100%
rename from browser/devtools/shared/Promise.jsm
rename to toolkit/devtools/_Promise.jsm
diff --git a/toolkit/devtools/debugger/dbg-client.jsm b/toolkit/devtools/debugger/dbg-client.jsm
index 8c5ab00308f4..86af464ae732 100644
--- a/toolkit/devtools/debugger/dbg-client.jsm
+++ b/toolkit/devtools/debugger/dbg-client.jsm
@@ -487,6 +487,7 @@ function ThreadClient(aClient, aActor) {
   this._frameCache = [];
   this._scriptCache = {};
   this._pauseGrips = {};
+  this._threadGrips = {};
 }
 
 ThreadClient.prototype = {
@@ -861,30 +862,74 @@ ThreadClient.prototype = {
   },
 
   /**
-   * Return an instance of LongStringClient for the given long string grip.
+   * Get or create a long string client, checking the grip client cache if it
+   * already exists.
+   *
+   * @param aGrip Object
+   *        The long string grip returned by the protocol.
+   * @param aGripCacheName String
+   *        The property name of the grip client cache to check for existing
+   *        clients in.
+   */
+  _longString: function TC__longString(aGrip, aGripCacheName) {
+    if (aGrip.actor in this[aGripCacheName]) {
+      return this[aGripCacheName][aGrip.actor];
+    }
+
+    let client = new LongStringClient(this._client, aGrip);
+    this[aGripCacheName][aGrip.actor] = client;
+    return client;
+  },
+
+  /**
+   * Return an instance of LongStringClient for the given long string grip that
+   * is scoped to the current pause.
    *
    * @param aGrip Object
    *        The long string grip returned by the protocol.
    */
-  longString: function TC_longString(aGrip) {
-    if (aGrip.actor in this._pauseGrips) {
-      return this._pauseGrips[aGrip.actor];
-    }
+  pauseLongString: function TC_pauseLongString(aGrip) {
+    return this._longString(aGrip, "_pauseGrips");
+  },
 
-    let client = new LongStringClient(this._client, aGrip);
-    this._pauseGrips[aGrip.actor] = client;
-    return client;
+  /**
+   * Return an instance of LongStringClient for the given long string grip that
+   * is scoped to the thread lifetime.
+   *
+   * @param aGrip Object
+   *        The long string grip returned by the protocol.
+   */
+  threadLongString: function TC_threadLongString(aGrip) {
+    return this._longString(aGrip, "_threadGrips");
+  },
+
+  /**
+   * Clear and invalidate all the grip clients from the given cache.
+   *
+   * @param aGripCacheName
+   *        The property name of the grip cache we want to clear.
+   */
+  _clearGripClients: function TC_clearGrips(aGripCacheName) {
+    for each (let grip in this[aGripCacheName]) {
+      grip.valid = false;
+    }
+    this[aGripCacheName] = {};
   },
 
   /**
    * Invalidate pause-lifetime grip clients and clear the list of
    * current grip clients.
    */
-  _clearPauseGrips: function TC_clearPauseGrips(aPacket) {
-    for each (let grip in this._pauseGrips) {
-      grip.valid = false;
-    }
-    this._pauseGrips = {};
+  _clearPauseGrips: function TC_clearPauseGrips() {
+    this._clearGripClients("_pauseGrips");
+  },
+
+  /**
+   * Invalidate pause-lifetime grip clients and clear the list of
+   * current grip clients.
+   */
+  _clearThreadGrips: function TC_clearPauseGrips() {
+    this._clearGripClients("_threadGrips");
   },
 
   /**
@@ -895,8 +940,17 @@ ThreadClient.prototype = {
     this._state = ThreadStateTypes[aPacket.type];
     this._clearFrames();
     this._clearPauseGrips();
+    aPacket.type === ThreadStateTypes.detached && this._clearThreadGrips();
     this._client._eventsEnabled && this.notify(aPacket.type, aPacket);
   },
+
+  /**
+   * Return an instance of SourceClient for the given actor.
+   */
+  source: function TC_source(aActor) {
+    return new SourceClient(this._client, aActor);
+  }
+
 };
 
 eventSource(ThreadClient.prototype);
@@ -1039,6 +1093,55 @@ LongStringClient.prototype = {
   }
 };
 
+/**
+ * A SourceClient provides a way to access the source text of a script.
+ *
+ * @param aClient DebuggerClient
+ *        The debugger client parent.
+ * @param aActor String
+ *        The name of the source actor.
+ */
+function SourceClient(aClient, aActor) {
+  this._actor = aActor;
+  this._client = aClient;
+}
+
+SourceClient.prototype = {
+  /**
+   * Get a long string grip for this SourceClient's source.
+   */
+  source: function SC_source(aCallback) {
+    let packet = {
+      to: this._actor,
+      type: "source"
+    };
+    this._client.request(packet, function (aResponse) {
+      if (aResponse.error) {
+        aCallback(aResponse);
+        return;
+      }
+
+      if (typeof aResponse.source === "string") {
+        aCallback(aResponse);
+        return;
+      }
+
+      let longString = this._client.activeThread.threadLongString(
+        aResponse.source);
+      longString.substring(0, longString.length, function (aResponse) {
+        if (aResponse.error) {
+          aCallback(aResponse);
+          return;
+        }
+
+        aCallback({
+          source: aResponse.substring
+        });
+      });
+    }.bind(this));
+  }
+};
+
 /**
  * Breakpoint clients are used to remove breakpoints that are no longer used.
  *
diff --git a/toolkit/devtools/debugger/server/dbg-script-actors.js b/toolkit/devtools/debugger/server/dbg-script-actors.js
index e8a8598c8c24..16a047db2f63 100644
--- a/toolkit/devtools/debugger/server/dbg-script-actors.js
+++ b/toolkit/devtools/debugger/server/dbg-script-actors.js
@@ -546,10 +546,12 @@ ThreadActor.prototype = {
         if (!this._scripts[url][i]) {
           continue;
         }
+
         let script = {
           url: url,
           startLine: i,
-          lineCount: this._scripts[url][i].lineCount
+          lineCount: this._scripts[url][i].lineCount,
+          source: this.sourceGrip(this._scripts[url][i], this)
         };
         scripts.push(script);
       }
@@ -781,13 +783,16 @@ ThreadActor.prototype = {
 
   /**
    * Create a grip for the given debuggee value.  If the value is an
-   * object, will create a pause-lifetime actor.
+   * object, will create an actor with the given lifetime.
    */
-  createValueGrip: function TA_createValueGrip(aValue) {
+  createValueGrip: function TA_createValueGrip(aValue, aPool=false) {
+    if (!aPool) {
+      aPool = this._pausePool;
+    }
     let type = typeof(aValue);
 
     if (type === "string" && this._stringIsLong(aValue)) {
-      return this.longStringGrip(aValue);
+      return this.longStringGrip(aValue, aPool);
     }
 
     if (type === "boolean" || type === "string" || type === "number") {
@@ -803,7 +808,7 @@ ThreadActor.prototype = {
     }
 
     if (typeof(aValue) === "object") {
-      return this.pauseObjectGrip(aValue);
+      return this.objectGrip(aValue, aPool);
     }
 
     dbg_assert(false, "Failed to provide a grip for: " + aValue);
@@ -881,26 +886,44 @@ ThreadActor.prototype = {
    *
    * @param aString String
    *        The string we are creating a grip for.
+   * @param aPool ActorPool
+   *        The actor pool where the new actor will be added.
    */
-  longStringGrip: function TA_longStringGrip(aString) {
-    if (!this._pausePool) {
-      throw new Error("LongString grip requested while not paused.");
+  longStringGrip: function TA_longStringGrip(aString, aPool) {
+    if (!aPool.longStringActors) {
+      aPool.longStringActors = {};
     }
 
-    if (!this._pausePool.longStringActors) {
-      this._pausePool.longStringActors = {};
-    }
-
-    if (this._pausePool.longStringActors.hasOwnProperty(aString)) {
-      return this._pausePool.longStringActors[aString].grip();
+    if (aPool.longStringActors.hasOwnProperty(aString)) {
+      return aPool.longStringActors[aString].grip();
     }
 
     let actor = new LongStringActor(aString, this);
-    this._pausePool.addActor(actor);
-    this._pausePool.longStringActors[aString] = actor;
+    aPool.addActor(actor);
+    aPool.longStringActors[aString] = actor;
     return actor.grip();
   },
 
+  /**
+   * Create a long string grip that is scoped to a pause.
+   *
+   * @param aString String
+   *        The string we are creating a grip for.
+   */
+  pauseLongStringGrip: function TA_pauseLongStringGrip (aString) {
+    return this.longStringGrip(aString, this._pausePool);
+  },
+
+  /**
+   * Create a long string grip that is scoped to a thread.
+   *
+   * @param aString String
+   *        The string we are creating a grip for.
+   */
+  threadLongStringGrip: function TA_pauseLongStringGrip (aString) {
+    return this.longStringGrip(aString, this._threadLifetimePool);
+  },
+
   /**
    * Returns true if the string is long enough to use a LongStringActor instead
    * of passing the value directly over the protocol.
@@ -912,6 +935,26 @@ ThreadActor.prototype = {
     return aString.length >= DebuggerServer.LONG_STRING_LENGTH;
   },
 
+  /**
+   * Create a source grip for the given script.
+   */
+  sourceGrip: function TA_sourceGrip(aScript) {
+    // TODO: Once we have Debugger.Source, this should be replaced with a
+    // weakmap mapping Debugger.Source instances to SourceActor instances.
+    if (!this.threadLifetimePool.sourceActors) {
+      this.threadLifetimePool.sourceActors = {};
+    }
+
+    if (this.threadLifetimePool.sourceActors[aScript.url]) {
+      return this.threadLifetimePool.sourceActors[aScript.url].grip();
+    }
+
+    let actor = new SourceActor(aScript, this);
+    this.threadLifetimePool.addActor(actor);
+    this.threadLifetimePool.sourceActors[aScript.url] = actor;
+    return actor.grip();
+  },
+
   // JS Debugger API hooks.
 
   /**
@@ -981,7 +1024,8 @@ ThreadActor.prototype = {
         type: "newScript",
         url: aScript.url,
         startLine: aScript.startLine,
-        lineCount: aScript.lineCount
+        lineCount: aScript.lineCount,
+        source: this.sourceGrip(aScript, this)
       });
     }
   },
@@ -1133,6 +1177,176 @@ function update(aTarget, aNewAttrs) {
 }
 
 
+/**
+ * A SourceActor provides information about the source of a script.
+ *
+ * @param aScript Debugger.Script
+ *        The script whose source we are representing.
+ * @param aThreadActor ThreadActor
+ *        The current thread actor.
+ */
+function SourceActor(aScript, aThreadActor) {
+  this._threadActor = aThreadActor;
+  this._script = aScript;
+}
+
+SourceActor.prototype = {
+  constructor: SourceActor,
+  actorPrefix: "source",
+
+  get threadActor() { return this._threadActor; },
+
+  grip: function SA_grip() {
+    return this.actorID;
+  },
+
+  disconnect: function LSA_disconnect() {
+    if (this.registeredPool && this.registeredPool.sourceActors) {
+      delete this.registeredPool.sourceActors[this.actorID];
+    }
+  },
+
+  /**
+   * Handler for the "source" packet.
+   */
+  onSource: function SA_onSource(aRequest) {
+    this
+      ._loadSource()
+      .chainPromise(function(aSource) {
+        return this._threadActor.createValueGrip(
+          aSource, this.threadActor.threadLifetimePool);
+      }.bind(this))
+      .chainPromise(function (aSourceGrip) {
+        return {
+          from: this.actorID,
+          source: aSourceGrip
+        };
+      }.bind(this))
+      .trap(function (aError) {
+        return {
+          "from": this.actorID,
+          "error": "loadSourceError",
+          "message": "Could not load the source for " + this._script.url + "."
+        };
+      }.bind(this))
+      .chainPromise(function (aPacket) {
+        this.conn.send(aPacket);
+      }.bind(this));
+  },
+
+  /**
+   * Convert a given string, encoded in a given character set, to unicode.
+   * @param string aString
+   *        A string.
+   * @param string aCharset
+   *        A character set.
+   * @return string
+   *         A unicode string.
+   */
+  _convertToUnicode: function SS__convertToUnicode(aString, aCharset) {
+    // Decoding primitives.
+    let converter = Cc["@mozilla.org/intl/scriptableunicodeconverter"]
+        .createInstance(Ci.nsIScriptableUnicodeConverter);
+
+    try {
+      converter.charset = aCharset || "UTF-8";
+      return converter.ConvertToUnicode(aString);
+    } catch(e) {
+      return aString;
+    }
+  },
+
+  /**
+   * Performs a request to load the desired URL and returns a promise.
+   *
+   * @param aURL String
+   *        The URL we will request.
+   * @returns Promise
+   *
+   * XXX: It may be better to use nsITraceableChannel to get to the sources
+   * without relying on caching when we can (not for eval, etc.):
+   * http://www.softwareishard.com/blog/firebug/nsitraceablechannel-intercept-http-traffic/
+   */
+  _loadSource: function SA__loadSource() {
+    let promise = new Promise();
+    let url = this._script.url;
+    let scheme;
+    try {
+      scheme = Services.io.extractScheme(url);
+    } catch (e) {
+      // In the xpcshell tests, the script url is the absolute path of the test
+      // file, which will make a malformed URI error be thrown. Add the file
+      // scheme prefix ourselves.
+      url = "file://" + url;
+      scheme = Services.io.extractScheme(url);
+    }
+
+    switch (scheme) {
+      case "file":
+      case "chrome":
+      case "resource":
+        try {
+          NetUtil.asyncFetch(url, function onFetch(aStream, aStatus) {
+            if (!Components.isSuccessCode(aStatus)) {
+              promise.reject(new Error("Request failed"));
+              return;
+            }
+
+            let source = NetUtil.readInputStreamToString(aStream, aStream.available());
+            promise.resolve(this._convertToUnicode(source));
+            aStream.close();
+          }.bind(this));
+        } catch (ex) {
+          promise.reject(new Error("Request failed"));
+        }
+        break;
+
+      default:
+        let channel;
+        try {
+          channel = Services.io.newChannel(url, null, null);
+        } catch (e if e.name == "NS_ERROR_UNKNOWN_PROTOCOL") {
+          // On Windows xpcshell tests, c:/foo/bar can pass as a valid URL, but
+          // newChannel won't be able to handle it.
+          url = "file:///" + url;
+          channel = Services.io.newChannel(url, null, null);
+        }
+        let chunks = [];
+        let streamListener = {
+          onStartRequest: function(aRequest, aContext, aStatusCode) {
+            if (!Components.isSuccessCode(aStatusCode)) {
+              promise.reject("Request failed");
+            }
+          },
+          onDataAvailable: function(aRequest, aContext, aStream, aOffset, aCount) {
+            chunks.push(NetUtil.readInputStreamToString(aStream, aCount));
+          },
+          onStopRequest: function(aRequest, aContext, aStatusCode) {
+            if (!Components.isSuccessCode(aStatusCode)) {
+              promise.reject("Request failed");
+              return;
+            }
+
+            promise.resolve(this._convertToUnicode(chunks.join(""),
+                                                   channel.contentCharset));
+          }.bind(this)
+        };
+
+        channel.loadFlags = channel.LOAD_FROM_CACHE;
+        channel.asyncOpen(streamListener, null);
+        break;
+    }
+
+    return promise;
+  }
+
+};
+
+SourceActor.prototype.requestTypes = {
+  "source": SourceActor.prototype.onSource
+};
+
+
 /**
  * Creates an actor for the specified object.
  *
diff --git a/toolkit/devtools/debugger/server/dbg-server.js b/toolkit/devtools/debugger/server/dbg-server.js
index 12370ef66f8f..4ff6acda6cf0 100644
--- a/toolkit/devtools/debugger/server/dbg-server.js
+++ b/toolkit/devtools/debugger/server/dbg-server.js
@@ -24,6 +24,8 @@ let wantLogging = Services.prefs.getBoolPref("devtools.debugger.log");
 Cu.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
 
+Cu.import("resource://gre/modules/devtools/_Promise.jsm");
+
 function dumpn(str) {
   if (wantLogging) {
     dump("DBG-SERVER: " + str + "\n");
diff --git a/toolkit/devtools/debugger/tests/unit/test_listscripts-01.js b/toolkit/devtools/debugger/tests/unit/test_listscripts-01.js
index d3e2ea402ae1..b18fa6f6a8aa 100644
--- a/toolkit/devtools/debugger/tests/unit/test_listscripts-01.js
+++ b/toolkit/devtools/debugger/tests/unit/test_listscripts-01.js
@@ -35,8 +35,9 @@ function test_simple_listscripts()
       // Check the return value.
       do_check_true(!!script);
       do_check_eq(script.url, path);
-      do_check_eq(script.startLine, 46);
+      do_check_eq(script.startLine, gDebuggee.line0);
       do_check_eq(script.lineCount, 4);
+      do_check_true(!!script.source);
       gThreadClient.resume(function () {
         finishClient(gClient);
       });
diff --git a/toolkit/devtools/debugger/tests/unit/test_longstringgrips-01.js b/toolkit/devtools/debugger/tests/unit/test_longstringgrips-01.js
index bdebd8578bf1..1e93aad24e57 100644
--- a/toolkit/devtools/debugger/tests/unit/test_longstringgrips-01.js
+++ b/toolkit/devtools/debugger/tests/unit/test_longstringgrips-01.js
@@ -48,7 +48,7 @@ function test_longstring_grip()
       do_check_eq(grip.length, longString.length);
       do_check_eq(grip.initial, longString.substr(0, DebuggerServer.LONG_STRING_INITIAL_LENGTH));
 
-      let longStringClient = gThreadClient.longString(grip);
+      let longStringClient = gThreadClient.pauseLongString(grip);
       longStringClient.substring(22, 28, function (aResponse) {
         try {
           do_check_eq(aResponse.substring, "monkey");
diff --git a/toolkit/devtools/debugger/tests/unit/test_longstringgrips-02.js b/toolkit/devtools/debugger/tests/unit/test_longstringgrips-02.js
index 5c49ce059f3f..1bb7271406d6 100644
--- a/toolkit/devtools/debugger/tests/unit/test_longstringgrips-02.js
+++ b/toolkit/devtools/debugger/tests/unit/test_longstringgrips-02.js
@@ -36,7 +36,7 @@ function test_longstring_grip()
         actor: "123fakeActor123",
         initial: ""
       };
-      let longStringClient = gThreadClient.longString(fakeLongStringGrip);
+      let longStringClient = gThreadClient.pauseLongString(fakeLongStringGrip);
       longStringClient.substring(22, 28, function (aResponse) {
         try {
           do_check_true(!!aResponse.error,
diff --git a/toolkit/devtools/debugger/tests/unit/test_source-01.js b/toolkit/devtools/debugger/tests/unit/test_source-01.js
new file mode 100644
index 000000000000..31582bf0af7c
--- /dev/null
+++ b/toolkit/devtools/debugger/tests/unit/test_source-01.js
@@ -0,0 +1,77 @@
+/* -*- Mode: javascript; js-indent-level: 2; -*- */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+var gDebuggee;
+var gClient;
+var gThreadClient;
+
+// This test ensures that we can create SourceActors and SourceClients properly,
+// and that they can communicate over the protocol to fetch the source text for
+// a given script.
+
+Cu.import("resource://gre/modules/NetUtil.jsm");
+
+function run_test()
+{
+  initTestDebuggerServer();
+  gDebuggee = addTestGlobal("test-grips");
+  gDebuggee.eval(function stopMe(arg1) {
+    debugger;
+  }.toString());
+
+  gClient = new DebuggerClient(DebuggerServer.connectPipe());
+  gClient.connect(function() {
+    attachTestGlobalClientAndResume(gClient, "test-grips", function(aResponse, aThreadClient) {
+      gThreadClient = aThreadClient;
+      gThreadClient.addListener("unsolicitedPause", unsolicitedPauseListener);
+      test_source();
+    });
+  });
+  do_test_pending();
+}
+
+function unsolicitedPauseListener(aEvent, aPacket, aContinue) {
+  gContinue = aContinue;
+}
+
+function test_source()
+{
+  DebuggerServer.LONG_STRING_LENGTH = 200;
+
+  gThreadClient.addOneTimeListener("paused", function(aEvent, aPacket) {
+    gThreadClient.getScripts(function (aResponse) {
+      do_check_true(!!aResponse);
+      do_check_true(!!aResponse.scripts);
+
+      let script = aResponse.scripts.filter(function (s) {
+        return s.url.match(/test_source-01.js$/);
+      })[0];
+
+      do_check_true(!!script);
+      do_check_true(!!script.source);
+
+      let sourceClient = gThreadClient.source(script.source);
+      sourceClient.source(function (aResponse) {
+        do_check_true(!!aResponse);
+        do_check_true(!aResponse.error);
+        do_check_true(!!aResponse.source);
+
+        let f = do_get_file("test_source-01.js", false);
+        let s = Cc["@mozilla.org/network/file-input-stream;1"]
+          .createInstance(Ci.nsIFileInputStream);
+        s.init(f, -1, -1, false);
+
+        do_check_eq(NetUtil.readInputStreamToString(s, s.available()),
+                    aResponse.source);
+
+        s.close();
+        gThreadClient.resume(function () {
+          finishClient(gClient);
+        });
+      });
+    });
+  });
+
+  gDebuggee.eval('stopMe()');
+}
diff --git a/toolkit/devtools/debugger/tests/unit/xpcshell.ini b/toolkit/devtools/debugger/tests/unit/xpcshell.ini
index e1644c033792..c00e85e612d4 100644
--- a/toolkit/devtools/debugger/tests/unit/xpcshell.ini
+++ b/toolkit/devtools/debugger/tests/unit/xpcshell.ini
@@ -64,4 +64,5 @@ tail =
 [test_longstringactor.js]
 [test_longstringgrips-01.js]
 [test_longstringgrips-02.js]
+[test_source-01.js]
 [test_breakpointstore.js]