bug 1149772 - never create fake HWND in child processes r=davidb

accessible/windows/msaa/nsWinUtils.cpp

@@ -9,6 +9,7 @@
 
 #include "Compatibility.h"
 #include "DocAccessible.h"
+#include "nsAccessibilityService.h"
 #include "nsCoreUtils.h"
 
 #include "mozilla/Preferences.h"
@@ -58,6 +59,9 @@ nsWinUtils::MaybeStartWindowEmulation()
 {
   // Register window class that'll be used for document accessibles associated
   // with tabs.
+  if (IPCAccessibilityActive())
+    return false;
+
   if (Compatibility::IsJAWS() || Compatibility::IsWE() ||
       Compatibility::IsDolphin() ||
       XRE_GetProcessType() == GeckoProcessType_Content) {