diff -r 000000000000 -r 6474c204b198 toolkit/modules/WindowDraggingUtils.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/modules/WindowDraggingUtils.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,110 @@
+/* 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/. */
+
+#ifdef XP_WIN
+#define USE_HITTEST
+#elifdef MOZ_WIDGET_COCOA
+#define USE_HITTEST
+#endif
+
+this.EXPORTED_SYMBOLS = [ "WindowDraggingElement" ];
+
+this.WindowDraggingElement = function WindowDraggingElement(elem) {
+  this._elem = elem;
+  this._window = elem.ownerDocument.defaultView;
+#ifdef USE_HITTEST
+  if (!this.isPanel())
+    this._elem.addEventListener("MozMouseHittest", this, false);
+  else
+#endif
+  this._elem.addEventListener("mousedown", this, false);
+};
+
+WindowDraggingElement.prototype = {
+  mouseDownCheck: function(e) { return true; },
+  dragTags: ["box", "hbox", "vbox", "spacer", "label", "statusbarpanel", "stack",
+             "toolbaritem", "toolbarseparator", "toolbarspring", "toolbarspacer",
+             "radiogroup", "deck", "scrollbox", "arrowscrollbox", "tabs"],
+  shouldDrag: function(aEvent) {
+    if (aEvent.button != 0 ||
+        this._window.fullScreen ||
+        !this.mouseDownCheck.call(this._elem, aEvent) ||
+        aEvent.defaultPrevented)
+      return false;
+
+    let target = aEvent.originalTarget, parent = aEvent.originalTarget;
+
+    // The target may be inside an embedded iframe or browser. (bug 615152)
+    if (target.ownerDocument.defaultView != this._window)
+      return false;
+
+    while (parent != this._elem) {
+      let mousethrough = parent.getAttribute("mousethrough");
+      if (mousethrough == "always")
+        target = parent.parentNode;
+      else if (mousethrough == "never")
+        break;
+      parent = parent.parentNode;
+    }
+    while (target != this._elem) {
+      if (this.dragTags.indexOf(target.localName) == -1)
+        return false;
+      target = target.parentNode;
+    }
+    return true;
+  },
+  isPanel : function() {
+    return this._elem instanceof Components.interfaces.nsIDOMXULElement &&
+           this._elem.localName == "panel";
+  },
+  handleEvent: function(aEvent) {
+    let isPanel = this.isPanel();
+#ifdef USE_HITTEST
+    if (!isPanel) {
+      if (this.shouldDrag(aEvent))
+        aEvent.preventDefault();
+      return;
+    }
+#endif
+
+    switch (aEvent.type) {
+      case "mousedown":
+        if (!this.shouldDrag(aEvent))
+          return;
+
+#ifdef MOZ_WIDGET_GTK
+        // On GTK, there is a toolkit-level function which handles
+        // window dragging, which must be used.
+        this._window.beginWindowMove(aEvent, isPanel ? this._elem : null);
+#else
+        if (isPanel) {
+          let screenRect = this._elem.getOuterScreenRect();
+          this._deltaX = aEvent.screenX - screenRect.left;
+          this._deltaY = aEvent.screenY - screenRect.top;
+        }
+        else {
+          this._deltaX = aEvent.screenX - this._window.screenX;
+          this._deltaY = aEvent.screenY - this._window.screenY;
+        }
+        this._draggingWindow = true;
+        this._window.addEventListener("mousemove", this, false);
+        this._window.addEventListener("mouseup", this, false);
+#endif
+        break;
+      case "mousemove":
+        if (this._draggingWindow) {
+          let toDrag = this.isPanel() ? this._elem : this._window;
+          toDrag.moveTo(aEvent.screenX - this._deltaX, aEvent.screenY - this._deltaY);
+        }
+        break;
+      case "mouseup":
+        if (this._draggingWindow) {
+          this._draggingWindow = false;
+          this._window.removeEventListener("mousemove", this, false);
+          this._window.removeEventListener("mouseup", this, false);
+        }
+        break;
+    }
+  }
+}