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diff --git a/docshell/base/nsIScrollable.idl b/docshell/base/nsIScrollable.idl
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+++ b/docshell/base/nsIScrollable.idl
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+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=2 sw=2 et tw=78:
+ *
+ * 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"
+
+/**
+ * The nsIScrollable is an interface that can be implemented by a control that
+ * supports scrolling.  This is a generic interface without concern for the 
+ * type of content that may be inside.
+ */
+[scriptable, uuid(3507fc93-313e-4a4c-8ca8-4d0ea0f97315)]
+interface nsIScrollable : nsISupports
+{
+  /**
+   * Constants declaring the two scroll orientations a scrollbar can be in.
+   * ScrollOrientation_X - Horizontal scrolling.  When passing this
+   *         in to a method you are requesting or setting data for the
+   *         horizontal scrollbar.
+   * ScrollOrientation_Y - Vertical scrolling.  When passing this
+   *         in to a method you are requesting or setting data for the
+   *         vertical scrollbar.
+   */
+  const long ScrollOrientation_X = 1;
+  const long ScrollOrientation_Y = 2;
+
+  /**
+   * Constants declaring the states of the scrollbars.
+   * ScrollPref_Auto - bars visible only when needed.
+   * ScrollPref_Never - bars never visible, even when scrolling still possible.
+   * ScrollPref_Always - bars always visible, even when scrolling is not possible
+   */
+  const long Scrollbar_Auto = 1;
+  const long Scrollbar_Never = 2;
+  const long Scrollbar_Always = 3;
+
+  /**
+   * Get or set the default scrollbar state for all documents in
+   * this shell.
+   */
+  long getDefaultScrollbarPreferences(in long scrollOrientation);
+  void setDefaultScrollbarPreferences(in long scrollOrientation,
+                                      in long scrollbarPref);
+
+  /**
+   * Get information about whether the vertical and horizontal scrollbars are
+   * currently visible.  If you are only interested in one of the visibility
+   * settings pass nullptr in for the one you aren't interested in.
+   */
+  void getScrollbarVisibility(out boolean verticalVisible,
+                              out boolean horizontalVisible);
+};