diff --git a/modules/libpref/src/nsPrefService.cpp b/modules/libpref/src/nsPrefService.cpp
index c5b60180512c..f0eee745469d 100644
--- a/modules/libpref/src/nsPrefService.cpp
+++ b/modules/libpref/src/nsPrefService.cpp
@@ -82,9 +82,6 @@ static PRBool isSharingEnabled();
 static nsresult openPrefFile(nsIFile* aFile);
 static nsresult pref_InitInitialObjects(void);
 
-  // needed so we can still get the JS Runtime Service during XPCOM shutdown
-static nsIJSRuntimeService* gJSRuntimeService = nsnull; // owning reference
-
 //-----------------------------------------------------------------------------
 
 /*
@@ -105,7 +102,6 @@ nsPrefService::~nsPrefService()
 {
   PREF_Cleanup();
   NS_IF_RELEASE(mCurrentFile);
-  NS_IF_RELEASE(gJSRuntimeService);
 
 #ifdef MOZ_PROFILESHARING
   NS_IF_RELEASE(mCurrentSharedFile);
diff --git a/modules/libpref/src/nsPrefService.h b/modules/libpref/src/nsPrefService.h
index b8de5519483a..4baa279741c7 100644
--- a/modules/libpref/src/nsPrefService.h
+++ b/modules/libpref/src/nsPrefService.h
@@ -36,6 +36,9 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
+#ifndef nsPrefService_h__
+#define nsPrefService_h__
+
 #include "nsIPrefService.h"
 #include "nsIPrefBranch.h"
 #include "nsIPrefBranchInternal.h"
@@ -82,3 +85,4 @@ private:
   nsIFile*                mCurrentSharedFile;
 };
 
+#endif // nsPrefService_h__
diff --git a/modules/libpref/src/nsPrefsFactory.cpp b/modules/libpref/src/nsPrefsFactory.cpp
index 01f18e19acb6..490ccdc833a3 100644
--- a/modules/libpref/src/nsPrefsFactory.cpp
+++ b/modules/libpref/src/nsPrefsFactory.cpp
@@ -40,6 +40,11 @@
 #include "nsPrefService.h"
 #include "nsPrefBranch.h"
 #include "nsIPref.h"
+#include "prefapi.h"
+
+#ifdef MOZ_PROFILESHARING
+#include "nsSharedPrefHandler.h"
+#endif
 
 // remove this when nsPref goes away
 extern NS_IMETHODIMP nsPrefConstructor(nsISupports *aOuter, REFNSIID aIID, void **aResult);
@@ -81,5 +86,15 @@ static const nsModuleComponentInfo components[] =
   },
 };
 
-NS_IMPL_NSGETMODULE(nsPrefModule, components)
+static void
+UnloadPrefsModule(nsIModule* unused)
+{
+  PREF_Cleanup();
 
+#ifdef MOZ_PROFILESHARING
+  NS_ASSERTION(!gSharedPrefHandler, "Leaking the shared pref handler (and the prefservice, presumably).");
+  gSharedPrefHandler = nsnull;
+#endif
+}
+
+NS_IMPL_NSGETMODULE_WITH_DTOR(nsPrefModule, components, UnloadPrefsModule)