diff --git a/xpcom/base/AvailableMemoryTracker.cpp b/xpcom/base/AvailableMemoryTracker.cpp
index b9939bdf83e4..a14c43bcbc45 100644
--- a/xpcom/base/AvailableMemoryTracker.cpp
+++ b/xpcom/base/AvailableMemoryTracker.cpp
@@ -34,8 +34,7 @@ namespace {
 
 #if defined(XP_WIN)
 
-#  if defined(__MINGW32__) || (NTDDI_VERSION < NTDDI_WINBLUE) || \
-      (NTDDI_VERSION == NTDDI_WINBLUE && !defined(WINBLUE_KBSPRING14))
+#  if defined(__MINGW32__)
 // Definitions for heap optimization that require the Windows SDK to target the
 // Windows 8.1 Update
 static const HEAP_INFORMATION_CLASS HeapOptimizeResources =
diff --git a/xpcom/base/nsSystemInfo.cpp b/xpcom/base/nsSystemInfo.cpp
index b4f129a1e677..b9b9ca136da0 100644
--- a/xpcom/base/nsSystemInfo.cpp
+++ b/xpcom/base/nsSystemInfo.cpp
@@ -930,7 +930,7 @@ nsresult CollectProcessInfo(ProcessInfo& info) {
   return NS_OK;
 }
 
-#if defined(XP_WIN) && (_WIN32_WINNT < 0x0A00) || defined(__MINGW32__)
+#if defined(__MINGW32__)
 WINBASEAPI
 BOOL WINAPI IsUserCetAvailableInEnvironment(_In_ DWORD UserCetEnvironment);
 
diff --git a/xpcom/glue/MemUtils.cpp b/xpcom/glue/MemUtils.cpp
index 531a5ea2f525..402568383c65 100644
--- a/xpcom/glue/MemUtils.cpp
+++ b/xpcom/glue/MemUtils.cpp
@@ -50,14 +50,7 @@ void mozilla::PrefetchMemory(uint8_t* aStart, size_t aNumBytes) {
 #elif defined(XP_WIN)
   MaybeInitPrefetchVirtualMemory();
   if (*sPrefetchVirtualMemory) {
-    // Normally, we'd use WIN32_MEMORY_RANGE_ENTRY, but that requires
-    // a different _WIN32_WINNT value before including windows.h, but
-    // that causes complications with unified sources. It's a simple
-    // enough struct anyways.
-    struct {
-      PVOID VirtualAddress;
-      SIZE_T NumberOfBytes;
-    } entry;
+    WIN32_MEMORY_RANGE_ENTRY entry;
     entry.VirtualAddress = aStart;
     entry.NumberOfBytes = aNumBytes;
     (*sPrefetchVirtualMemory)(GetCurrentProcess(), 1, &entry, 0);
diff --git a/xpcom/io/SpecialSystemDirectory.cpp b/xpcom/io/SpecialSystemDirectory.cpp
index fcb366aede1a..2abbbe4c0aab 100644
--- a/xpcom/io/SpecialSystemDirectory.cpp
+++ b/xpcom/io/SpecialSystemDirectory.cpp
@@ -93,25 +93,6 @@ static nsresult GetWindowsFolder(int aFolder, nsIFile** aFile) {
   return NS_NewLocalFile(nsDependentString(path, len), true, aFile);
 }
 
-#  if WINVER < 0x0601
-__inline HRESULT SHLoadLibraryFromKnownFolder(REFKNOWNFOLDERID aFolderId,
-                                              DWORD aMode, REFIID riid,
-                                              void** ppv) {
-  *ppv = nullptr;
-  IShellLibrary* plib;
-  HRESULT hr = CoCreateInstance(CLSID_ShellLibrary, nullptr,
-                                CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&plib));
-  if (SUCCEEDED(hr)) {
-    hr = plib->LoadLibraryFromKnownFolder(aFolderId, aMode);
-    if (SUCCEEDED(hr)) {
-      hr = plib->QueryInterface(riid, ppv);
-    }
-    plib->Release();
-  }
-  return hr;
-}
-#  endif
-
 #  if defined(MOZ_THUNDERBIRD) || defined(MOZ_SUITE)
 /*
  * Return the default save-to location for the Windows Library passed in