new file mode 100644
--- /dev/null
+++ b/ipc/mscom/COMApartmentRegion.h
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_mscom_COMApartmentRegion_h
+#define mozilla_mscom_COMApartmentRegion_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+
+#include <objbase.h>
+
+namespace mozilla {
+namespace mscom {
+
+template<COINIT T>
+class MOZ_RAII COMApartmentRegion
+{
+public:
+  COMApartmentRegion()
+    : mInitResult(::CoInitializeEx(nullptr, T))
+  {
+    // If this fires then we're probably mixing apartments on the same thread
+    MOZ_ASSERT(IsValid());
+  }
+
+  ~COMApartmentRegion()
+  {
+    if (IsValid()) {
+      ::CoUninitialize();
+    }
+  }
+
+  bool IsValidOutermost() const
+  {
+    return mInitResult == S_OK;
+  }
+
+  bool IsValid() const
+  {
+    return SUCCEEDED(mInitResult);
+  }
+
+private:
+  COMApartmentRegion(const COMApartmentRegion&) = delete;
+  COMApartmentRegion& operator=(const COMApartmentRegion&) = delete;
+  COMApartmentRegion(COMApartmentRegion&&) = delete;
+  COMApartmentRegion& operator=(COMApartmentRegion&&) = delete;
+
+  HRESULT mInitResult;
+};
+
+typedef COMApartmentRegion<COINIT_APARTMENTTHREADED> STARegion;
+typedef COMApartmentRegion<COINIT_MULTITHREADED> MTARegion;
+
+} // namespace mscom
+} // namespace mozilla
+
+#endif // mozilla_mscom_COMApartmentRegion_h
+

--- a/ipc/mscom/moz.build
+++ b/ipc/mscom/moz.build
@@ -1,15 +1,16 @@
 # -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
 # vim: set filetype=python:
 # 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/.
 
 EXPORTS.mozilla.mscom += [
+    'COMApartmentRegion.h',
 ]
 
 UNIFIED_SOURCES += [
 ]
 
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'