diff -r 000000000000 -r 6474c204b198 widget/nsIScreenManager.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/nsIScreenManager.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,57 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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/. */
+
+#include "nsISupports.idl"
+#include "nsIScreen.idl"
+
+[scriptable, uuid(1C195990-FF9E-412B-AFE7-67D1C660BB27)]
+interface nsIScreenManager : nsISupports
+{
+    //
+    // Returns the screen that contains the rectangle. If the rect overlaps
+    // multiple screens, it picks the screen with the greatest area of intersection.
+    //
+    // The coordinates are in pixels (not twips) and in screen coordinates.
+    //
+  nsIScreen screenForRect ( in long left, in long top, in long width, in long height ) ;
+  
+    // The screen with the menubar/taskbar. This shouldn't be needed very
+    // often.
+  readonly attribute nsIScreen primaryScreen;
+  
+    // Holds the number of screens that are available
+  readonly attribute unsigned long numberOfScreens;
+
+    // The default DPI scaling factor of the screen environment (number of
+    // screen pixels corresponding to 1 CSS px, at the default zoom level).
+    //
+    // This is currently fixed at 1.0 on most platforms, but varies on Windows
+    // if the "logical DPI" scaling option in the Display control panel is set
+    // to a value other than 100% (e.g. 125% or 150% are increasingly common
+    // defaults on laptops with high-dpi screens). See bug 851520.
+    //
+    // NOTE that on OS X, this does -not- reflect the "backing scale factor"
+    // used to support Retina displays, which is a per-display property,
+    // not a system-wide scaling factor. The default ratio of CSS pixels to
+    // Cocoa points remains 1:1, even on a Retina screen where one Cocoa point
+    // corresponds to two device pixels. (This is exposed via other APIs:
+    // see window.devicePixelRatio).
+    //
+    // NOTE also that on Linux, this does -not- currently reflect changes
+    // to the system-wide (X11 or Gtk2) DPI value, as Firefox does not yet
+    // honor these settings. See bug 798362 and bug 712898.
+  readonly attribute float systemDefaultScale;
+
+    // Returns the nsIScreen instance for the given native widget pointer;
+    // the pointer is specific to the particular widget implementation,
+    // and is generally of the same type that NS_NATIVE_WINDOW is.
+  [noscript] nsIScreen screenForNativeWidget ( in voidPtr nativeWidget );
+};
+
+
+%{ C++
+
+%}