diff --git a/xpcom/glue/nsCategoryCache.cpp b/xpcom/glue/nsCategoryCache.cpp
--- a/xpcom/glue/nsCategoryCache.cpp
+++ b/xpcom/glue/nsCategoryCache.cpp
@@ -58,51 +58,53 @@ nsCategoryObserver::nsCategoryObserver(c
     do_GetService(NS_CATEGORYMANAGER_CONTRACTID);
   if (!catMan)
     return;
 
   nsCOMPtr<nsISimpleEnumerator> enumerator;
   nsresult rv = catMan->EnumerateCategory(aCategory,
                                           getter_AddRefs(enumerator));
   if (NS_FAILED(rv))
     return;
 
+  nsTArray<nsCString> entries;
   nsCOMPtr<nsISupports> entry;
   while (NS_SUCCEEDED(enumerator->GetNext(getter_AddRefs(entry)))) {
     nsCOMPtr<nsISupportsCString> entryName = do_QueryInterface(entry, &rv);
 
     if (NS_SUCCEEDED(rv)) {
       nsCAutoString categoryEntry;
       rv = entryName->GetData(categoryEntry);
 
       nsCString entryValue;
       catMan->GetCategoryEntry(aCategory,
                                categoryEntry.get(),
                                getter_Copies(entryValue));
 
       if (NS_SUCCEEDED(rv)) {
         mHash.Put(categoryEntry, entryValue);
-        mListener->EntryAdded(entryValue);
+        entries.AppendElement(entryValue);
       }
     }
   }
 
   // Now, listen for changes
   nsCOMPtr<nsIObserverService> serv =
     do_GetService(NS_OBSERVERSERVICE_CONTRACTID);
-  if (!serv)
-    return;
+  if (serv) {
+    serv->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, PR_FALSE);
+    serv->AddObserver(this, NS_XPCOM_CATEGORY_ENTRY_ADDED_OBSERVER_ID, PR_FALSE);
+    serv->AddObserver(this, NS_XPCOM_CATEGORY_ENTRY_REMOVED_OBSERVER_ID, PR_FALSE);
+    serv->AddObserver(this, NS_XPCOM_CATEGORY_CLEARED_OBSERVER_ID, PR_FALSE);
+  }
 
-  serv->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, PR_FALSE);
-
-  serv->AddObserver(this, NS_XPCOM_CATEGORY_ENTRY_ADDED_OBSERVER_ID, PR_FALSE);
-  serv->AddObserver(this, NS_XPCOM_CATEGORY_ENTRY_REMOVED_OBSERVER_ID, PR_FALSE);
-  serv->AddObserver(this, NS_XPCOM_CATEGORY_CLEARED_OBSERVER_ID, PR_FALSE);
+  for (PRUint32 entries.Length(); i-- > 0; )
+    mListener->EntryAdded(entryValue);
 }
 
 nsCategoryObserver::~nsCategoryObserver() {
 }
 
 NS_IMPL_ISUPPORTS1(nsCategoryObserver, nsIObserver)
 
 void
 nsCategoryObserver::ListenerDied() {
   mListener = nsnull;