--- a/js/xpconnect/src/XPCMaps.cpp
+++ b/js/xpconnect/src/XPCMaps.cpp
@@ -197,24 +197,51 @@ IID2NativeInterfaceMap::SizeOfIncludingT
     }
     return n;
 }
 
 /***************************************************************************/
 // implement ClassInfo2NativeSetMap...
 
 // static
+bool ClassInfo2NativeSetMap::Entry::Match(const PLDHashEntryHdr* aEntry,
+                                          const void* aKey)
+{
+    return static_cast<const Entry*>(aEntry)->key == aKey;
+}
+
+// static
+void ClassInfo2NativeSetMap::Entry::Clear(PLDHashTable* aTable,
+                                          PLDHashEntryHdr* aEntry)
+{
+    auto entry = static_cast<Entry*>(aEntry);
+    NS_RELEASE(entry->value);
+
+    entry->key = nullptr;
+    entry->value = nullptr;
+}
+
+const PLDHashTableOps ClassInfo2NativeSetMap::Entry::sOps =
+{
+    PLDHashTable::HashVoidPtrKeyStub,
+    Match,
+    PLDHashTable::MoveEntryStub,
+    Clear,
+    nullptr
+};
+
+// static
 ClassInfo2NativeSetMap*
 ClassInfo2NativeSetMap::newMap(int length)
 {
     return new ClassInfo2NativeSetMap(length);
 }
 
 ClassInfo2NativeSetMap::ClassInfo2NativeSetMap(int length)
-  : mTable(PLDHashTable::StubOps(), sizeof(Entry), length)
+  : mTable(&ClassInfo2NativeSetMap::Entry::sOps, sizeof(Entry), length)
 {
 }
 
 size_t
 ClassInfo2NativeSetMap::ShallowSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf)
 {
     size_t n = mallocSizeOf(this);
     n += mTable.ShallowSizeOfExcludingThis(mallocSizeOf);

--- a/js/xpconnect/src/XPCMaps.h
+++ b/js/xpconnect/src/XPCMaps.h
@@ -273,17 +273,22 @@ private:
 /*************************/
 
 class ClassInfo2NativeSetMap
 {
 public:
     struct Entry : public PLDHashEntryHdr
     {
         nsIClassInfo* key;
-        XPCNativeSet* value;
+        XPCNativeSet* value; // strong reference
+        static const PLDHashTableOps sOps;
+
+    private:
+        static bool Match(const PLDHashEntryHdr* aEntry, const void* aKey);
+        static void Clear(PLDHashTable* aTable, PLDHashEntryHdr* aEntry);
     };
 
     static ClassInfo2NativeSetMap* newMap(int length);
 
     inline XPCNativeSet* Find(nsIClassInfo* info)
     {
         auto entry = static_cast<Entry*>(mTable.Search(info));
         return entry ? entry->value : nullptr;
@@ -293,17 +298,17 @@ public:
     {
         NS_PRECONDITION(info,"bad param");
         auto entry = static_cast<Entry*>(mTable.Add(info, mozilla::fallible));
         if (!entry)
             return nullptr;
         if (entry->key)
             return entry->value;
         entry->key = info;
-        entry->value = set;
+        NS_ADDREF(entry->value = set);
         return set;
     }
 
     inline void Remove(nsIClassInfo* info)
     {
         NS_PRECONDITION(info,"bad param");
         mTable.Remove(info);
     }