--- a/content/media/nsMediaCache.cpp
+++ b/content/media/nsMediaCache.cpp
@@ -554,19 +554,33 @@ nsMediaCache::Init()
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
   nsCOMPtr<nsIFile> tmp;
   nsresult rv = NS_GetSpecialDirectory(NS_OS_TEMP_DIR, getter_AddRefs(tmp));
   if (NS_FAILED(rv))
     return rv;
   nsCOMPtr<nsILocalFile> tmpFile = do_QueryInterface(tmp);
+
+  // We put the media cache file in
+  // ${TempDir}/mozilla-media-cache/media_cache
   if (!tmpFile)
     return NS_ERROR_FAILURE;
-  rv = tmpFile->AppendNative(nsDependentCString("moz_media_cache"));
+  rv = tmpFile->AppendNative(nsDependentCString("mozilla-media-cache"));
+  if (NS_FAILED(rv))
+    return rv;
+  rv = tmpFile->Create(nsIFile::DIRECTORY_TYPE, 0600);
+  if (NS_FAILED(rv) && rv != NS_ERROR_FILE_ALREADY_EXISTS)
+    return rv;
+
+  rv = tmpFile->Create(nsIFile::DIRECTORY_TYPE, 0600);
+  if (NS_FAILED(rv) && rv != NS_ERROR_FILE_ALREADY_EXISTS)
+    return rv;
+
+  rv = tmpFile->AppendNative(nsDependentCString("media_cache"));
   if (NS_FAILED(rv))
     return rv;
   rv = tmpFile->CreateUnique(nsIFile::NORMAL_FILE_TYPE, 0600);
   if (NS_FAILED(rv))
     return rv;
   rv = tmpFile->OpenNSPRFileDesc(PR_RDWR | nsILocalFile::DELETE_ON_CLOSE,
                                  PR_IRWXU, &mFD);
   if (NS_FAILED(rv))

--- a/xpcom/build/nsXPComInit.cpp
+++ b/xpcom/build/nsXPComInit.cpp
@@ -174,16 +174,20 @@ static BrowserProcessSubThread* sIOThrea
 // Registry Factory creation function defined in nsRegistry.cpp
 // We hook into this function locally to create and register the registry
 // Since noone outside xpcom needs to know about this and nsRegistry.cpp
 // does not have a local include file, we are putting this definition
 // here rather than in nsIRegistry.h
 extern nsresult NS_RegistryGetFactory(nsIFactory** aFactory);
 extern nsresult NS_CategoryManagerGetFactory( nsIFactory** );
 
+#ifdef XP_WIN
+extern nsresult nsMediaCacheRemover_Startup();
+#endif
+
 #ifdef DEBUG
 extern void _FreeAutoLockStatics();
 #endif
 
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsProcess)
 
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsSupportsIDImpl)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsSupportsStringImpl)
@@ -550,17 +554,20 @@ NS_InitXPCOM2(nsIServiceManager* *result
     mozilla::scache::StartupCache::GetSingleton();
 #endif
     NS_TIME_FUNCTION_MARK("Next: create services from category");
 
     // Notify observers of xpcom autoregistration start
     NS_CreateServicesFromCategory(NS_XPCOM_STARTUP_CATEGORY, 
                                   nsnull,
                                   NS_XPCOM_STARTUP_OBSERVER_ID);
-    
+#ifdef XP_WIN
+    nsMediaCacheRemover_Startup();
+#endif
+
     return NS_OK;
 }
 
 
 //
 // NS_ShutdownXPCOM()
 //
 // The shutdown sequence for xpcom would be

--- a/xpcom/io/Makefile.in
+++ b/xpcom/io/Makefile.in
@@ -89,17 +89,17 @@ CPPSRCS += \
 		nsFastLoadService.cpp \
 		$(NULL)
 endif
 
 ifeq ($(MOZ_WIDGET_TOOLKIT),os2)
 CPPSRCS		+= nsLocalFileOS2.cpp
 else
 ifeq ($(MOZ_WIDGET_TOOLKIT),windows)
-CPPSRCS		+= nsLocalFileWin.cpp
+CPPSRCS		+= nsLocalFileWin.cpp nsMediaCacheRemover.cpp
 else
 CPPSRCS		+= nsLocalFileUnix.cpp
 endif # windows
 endif # OS2
 
 EXPORTS		= \
 		nsAppDirectoryServiceDefs.h \
 		nsDirectoryService.h \

new file mode 100644
--- /dev/null
+++ b/xpcom/io/nsMediaCacheRemover.cpp
@@ -0,0 +1,132 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Mozilla code.
+ *
+ * The Initial Developer of the Original Code is
+ * the Mozilla Foundation.
+ * Portions created by the Initial Developer are Copyright (C) 2010
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *   Chris Pearce <chris@pearce.org.nz>
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+#ifndef XP_WIN
+#error nsMediaCacheRemover only needed on Windows.
+#endif
+
+#include "nsIObserver.h"
+#include "nsIIdleService.h"
+#include "nsISimpleEnumerator.h"
+#include "nsILocalFile.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsString.h"
+#include "nsAutoPtr.h"
+
+// Duration of idle time before we'll get a callback whereupon we attempt to
+// remove any stray and unused media cache temp files.
+#define TEMP_FILE_IDLE_TIME 30
+
+// This class is instantiated during the xpcom initialization, and adds itself
+// as an idle observer. When the application has been idle for about 30 seconds
+// we'll get a notification, whereupon we'll attempt to delete
+// ${TempDir}/mozilla-media-cache/. This is to ensure all media cache temp
+// files which were supposed to be deleted on application exit were actually
+// deleted as they may not be if we previously crashed. See bug 572579. This
+// is only needed on some versions of Windows, nsILocalFile::DELETE_ON_CLOSE
+// works on other platforms.
+class nsMediaCacheRemover : public nsIObserver {
+public:
+  NS_DECL_ISUPPORTS
+
+  nsMediaCacheRemover() {
+    MOZ_COUNT_CTOR(nsMediaCacheRemover);
+  }
+
+  ~nsMediaCacheRemover() {
+    MOZ_COUNT_DTOR(nsMediaCacheRemover);
+  }
+
+  NS_IMETHODIMP Observe(nsISupports *subject,
+                        const char *topic,
+                        const PRUnichar *data)
+  {
+    if (strcmp(topic, "idle") == 0) {
+      // The user has been idle for a while, clean up the temp files.
+      // The idle service will drop its reference to this object after
+      // we exit, destroying this object.
+      RemoveMediaCacheFiles();
+    }
+    return NS_OK;
+  }
+
+  nsresult RegisterIdleObserver() {
+    // Add this as an idle observer. When we've been idle for 
+    // TEMP_FILE_IDLE_TIME seconds, we'll get a notification, and we'll then
+    // try to delete any stray media cache temp files.
+    nsCOMPtr<nsIIdleService> idleSvc =
+      do_GetService("@mozilla.org/widget/idleservice;1");
+    if (!idleSvc)
+      return NS_ERROR_FAILURE;
+    return idleSvc->AddIdleObserver(this, TEMP_FILE_IDLE_TIME);
+  }
+
+  void RemoveMediaCacheFiles() {
+    nsCOMPtr<nsIIdleService> idleSvc =
+      do_GetService("@mozilla.org/widget/idleservice;1");
+    if (idleSvc)
+      idleSvc->RemoveIdleObserver(this, TEMP_FILE_IDLE_TIME);
+
+    nsCOMPtr<nsIFile> tmpDir;
+    nsresult rv = NS_GetSpecialDirectory(NS_OS_TEMP_DIR,
+                                         getter_AddRefs(tmpDir));
+    if (NS_FAILED(rv))
+      return;
+    rv = tmpDir->AppendNative(nsDependentCString("mozilla-media-cache"));
+    if (NS_FAILED(rv))
+      return;
+
+    nsCOMPtr<nsILocalFile> tmpFile = do_QueryInterface(tmpDir);
+    if (!tmpFile)
+      return;
+
+    // Remove the directory recursively.  
+    tmpFile->Remove(PR_TRUE);
+  }
+};
+
+NS_IMPL_ISUPPORTS1(nsMediaCacheRemover, nsIObserver)
+
+nsresult nsMediaCacheRemover_Startup() {
+  // Create a new nsMediaCacheRemover, and register it as an idle observer.
+  // If it is successfully registered as an idle observer, its owning reference
+  // will be held by the idle service, otherwise it will be destroyed by the
+  // refptr here when it goes out of scope.
+  nsRefPtr<nsMediaCacheRemover> t = new nsMediaCacheRemover();
+  return t->RegisterIdleObserver();
+}