diff -r 000000000000 -r 6474c204b198 dom/interfaces/events/nsIDOMWheelEvent.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/interfaces/events/nsIDOMWheelEvent.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set 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/. */
+
+#include "nsIDOMMouseEvent.idl"
+
+[scriptable, builtinclass, uuid(86e2b577-7e61-4ed5-8ddd-c1533bf07137)]
+interface nsIDOMWheelEvent : nsIDOMMouseEvent
+{
+  const unsigned long DOM_DELTA_PIXEL = 0x00;
+  const unsigned long DOM_DELTA_LINE  = 0x01;
+  const unsigned long DOM_DELTA_PAGE  = 0x02;
+
+  // Note that DOM Level 3 Events defines the type of delta values as float.
+  // However, we should use double for them.  Javascript engine always uses
+  // double even if interface attributes are float.  If we defined them
+  // as float, that would cause error at casting from float to double.
+  // E.g., following function may return false if the deltaX is float:
+  //
+  // function () {
+  //   var event = new WheelEvent("wheel", { deltaX: 0.1 });
+  //   return (event.deltaX == 0.1);
+  // }
+
+  readonly attribute double        deltaX;
+  readonly attribute double        deltaY;
+  readonly attribute double        deltaZ;
+  readonly attribute unsigned long deltaMode;
+
+  [noscript] void initWheelEvent(in DOMString typeArg,
+                                 in boolean canBubbleArg,
+                                 in boolean cancelableArg,
+                                 in nsIDOMWindow viewArg,
+                                 in long detailArg,
+                                 in long screenXArg,
+                                 in long screenYArg,
+                                 in long clientXArg,
+                                 in long clientYArg,
+                                 in unsigned short buttonArg,
+                                 in nsIDOMEventTarget relatedTargetArg,
+                                 in DOMString modifiersListArg,
+                                 in double deltaXArg,
+                                 in double deltaYArg,
+                                 in double deltaZArg,
+                                 in unsigned long deltaMode);
+};