--- a/accessible/windows/msaa/RootAccessibleWrap.cpp
+++ b/accessible/windows/msaa/RootAccessibleWrap.cpp
@@ -1,16 +1,17 @@
 /* -*- Mode: C++; 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 "RootAccessibleWrap.h"
 
 #include "Compatibility.h"
+#include "mozilla/WindowsVersion.h"
 #include "nsCoreUtils.h"
 #include "nsWinUtils.h"
 
 using namespace mozilla::a11y;
 
 ////////////////////////////////////////////////////////////////////////////////
 // Constructor/destructor
 
@@ -150,18 +151,21 @@ RootAccessibleWrap::accNavigate(
   return S_OK;
 }
 
 STDMETHODIMP
 RootAccessibleWrap::get_accFocus(
       /* [retval][out] */ VARIANT __RPC_FAR *pvarChild)
 {
   HRESULT hr = DocAccessibleWrap::get_accFocus(pvarChild);
-  if (FAILED(hr) || pvarChild->vt != VT_EMPTY) {
-    // We got a definite result (either failure or an accessible).
+  if (FAILED(hr) || pvarChild->vt != VT_EMPTY || !IsWin8OrLater()) {
+    // 1. We got a definite result (either failure or an accessible); or
+    // 2. This is Windows 7, where we don't want to retrieve the focus from a
+    // remote document because this causes mysterious intermittent crashes
+    // when we're called by UIA clients; see bug 1424505.
     return hr;
   }
 
   // The base implementation reported no focus.
   // Focus might be in a remote document.
   // (The base implementation can't handle this.)
   // Get the document in the active tab.
   ProxyAccessible* docProxy = GetPrimaryRemoteTopLevelContentDoc();