--- a/b2g/chrome/content/desktop.js
+++ b/b2g/chrome/content/desktop.js
@@ -133,31 +133,31 @@ function initResponsiveDesign() {
     responsive.rotatebutton.addEventListener('command', function (evt) {
       GlobalSimulatorScreen.flipScreen();
       evt.stopImmediatePropagation();
       evt.preventDefault();
     }, true);
 
     // Enable touch events
     responsive.enableTouch();
+
+    // Automatically toggle responsive design mode
+    let width = 320, height = 480;
+    // We have to take into account padding and border introduced with the
+    // device look'n feel:
+    width += 15*2; // Horizontal padding
+    width += 1*2; // Vertical border
+    height += 60; // Top Padding
+    height += 1; // Top border
+    responsive.setSize(width, height);
   });
 
-  // Automatically toggle responsive design mode
-  let width = 320, height = 480;
-  // We have to take into account padding and border introduced with the
-  // device look'n feel:
-  width += 15*2; // Horizontal padding
-  width += 1*2; // Vertical border
-  height += 60; // Top Padding
-  height += 1; // Top border
-  let args = {'width': width, 'height': height};
+
   let mgr = browserWindow.ResponsiveUI.ResponsiveUIManager;
   mgr.toggle(browserWindow, browserWindow.gBrowser.selectedTab);
-  let responsive = browserWindow.gBrowser.selectedTab.__responsiveUI;
-  responsive.setSize(width, height);
 
 }
 
 function openDevtools() {
   // Open devtool panel while maximizing its size according to screen size
   Services.prefs.setIntPref('devtools.toolbox.sidebar.width',
                             browserWindow.outerWidth - 550);
   Services.prefs.setCharPref('devtools.toolbox.host', 'side');

--- a/b2g/dev/app/moz.build
+++ b/b2g/dev/app/moz.build
@@ -2,10 +2,11 @@
 # 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/.
 
 DIST_SUBDIR = 'browser'
 export('DIST_SUBDIR')
 
 JS_PREFERENCE_FILES += [
     '/b2g/app/b2g.js',
+    '/b2g/dev/app/mulet.js',
 ]
 

new file mode 100644
--- /dev/null
+++ b/b2g/dev/app/mulet.js
@@ -0,0 +1,19 @@
+// Automatically open b2g in a tab
+pref("browser.startup.homepage", "chrome://b2g/content/shell.html");
+
+// Disable some painful behavior of fx
+pref("startup.homepage_welcome_url", "");
+pref("browser.shell.checkDefaultBrowser", "");
+pref("browser.sessionstore.max_tabs_undo", 0);
+pref("browser.sessionstore.max_windows_undo", 0);
+pref("browser.sessionstore.restore_on_demand", false);
+pref("browser.sessionstore.resume_from_crash", false);
+
+// Display the devtools on the right of the phone
+pref("devtools.toolbox.host", "side");
+pref("devtools.toolbox.sidebar.width", 800);
+
+// Disable e10s as we don't want to run shell.html,
+// nor the system app OOP, but only inner apps
+pref("browser.tabs.remote.autostart", false);
+pref("browser.tabs.remote.autostart.1", false);