--- a/xpcom/build/XPCOMInit.cpp
+++ b/xpcom/build/XPCOMInit.cpp
@@ -106,17 +106,16 @@ extern nsresult nsStringInputStreamConst
 
 #include "nsUUIDGenerator.h"
 
 #include "nsIOUtil.h"
 
 #include "SpecialSystemDirectory.h"
 
 #if defined(XP_WIN)
-#include "mozilla/WindowsVersion.h"
 #include "nsWindowsRegKey.h"
 #endif
 
 #ifdef MOZ_WIDGET_COCOA
 #include "nsMacUtilsImpl.h"
 #endif
 
 #include "nsSystemInfo.h"

--- a/xpcom/glue/nsThreadUtils.cpp
+++ b/xpcom/glue/nsThreadUtils.cpp
@@ -15,25 +15,20 @@
 #else
 # include "nsXPCOMCIDInternal.h"
 # include "nsIThreadManager.h"
 # include "nsServiceManagerUtils.h"
 #endif
 
 #ifdef XP_WIN
 #include <windows.h>
-#include "mozilla/WindowsVersion.h"
-using mozilla::IsVistaOrLater;
 #elif defined(XP_MACOSX)
 #include <sys/resource.h>
 #endif
 
-#include <pratom.h>
-#include <prthread.h>
-
 using namespace mozilla;
 
 #ifndef XPCOM_GLUE_AVOID_NSPR
 
 NS_IMPL_ISUPPORTS(IdlePeriod, nsIIdlePeriod)
 
 NS_IMETHODIMP
 IdlePeriod::GetIdlePeriodHint(TimeStamp* aIdleDeadline)
@@ -407,18 +402,17 @@ nsThreadPoolNaming::GetNextThreadName(co
   name.AppendInt(++mCounter, 10); // The counter is declared as atomic
   return name;
 }
 
 // nsAutoLowPriorityIO
 nsAutoLowPriorityIO::nsAutoLowPriorityIO()
 {
 #if defined(XP_WIN)
-  lowIOPrioritySet = IsVistaOrLater() &&
-                     SetThreadPriority(GetCurrentThread(),
+  lowIOPrioritySet = SetThreadPriority(GetCurrentThread(),
                                        THREAD_MODE_BACKGROUND_BEGIN);
 #elif defined(XP_MACOSX)
   oldPriority = getiopolicy_np(IOPOL_TYPE_DISK, IOPOL_SCOPE_THREAD);
   lowIOPrioritySet = oldPriority != -1 &&
                      setiopolicy_np(IOPOL_TYPE_DISK,
                                     IOPOL_SCOPE_THREAD,
                                     IOPOL_THROTTLE) != -1;
 #else