--- a/toolkit/components/url-classifier/Classifier.cpp
+++ b/toolkit/components/url-classifier/Classifier.cpp
@@ -388,25 +388,32 @@ Classifier::TableRequest(nsACString& aRe
 
   // Generating v2 table info.
   nsTArray<nsCString> tables;
   ActiveTables(tables);
   for (uint32_t i = 0; i < tables.Length(); i++) {
     HashStore store(tables[i], GetProvider(tables[i]), mRootStoreDirectory);
 
     nsresult rv = store.Open();
-    if (NS_FAILED(rv))
+    if (NS_FAILED(rv)) {
       continue;
+    }
+
+    ChunkSet &adds = store.AddChunks();
+    ChunkSet &subs = store.SubChunks();
+
+    // Open HashStore will always succeed even that is not a v2 table.
+    // So skip tables without add and sub chunks.
+    if (adds.Length() == 0 && subs.Length() == 0) {
+      continue;
+    }
 
     aResult.Append(store.TableName());
     aResult.Append(';');
 
-    ChunkSet &adds = store.AddChunks();
-    ChunkSet &subs = store.SubChunks();
-
     if (adds.Length() > 0) {
       aResult.AppendLiteral("a:");
       nsAutoCString addList;
       adds.Serialize(addList);
       aResult.Append(addList);
     }
 
     if (subs.Length() > 0) {
@@ -917,67 +924,87 @@ Classifier::DropStores()
 }
 
 nsresult
 Classifier::RegenActiveTables()
 {
   mActiveTablesCache.Clear();
 
   nsTArray<nsCString> foundTables;
-  ScanStoreDir(foundTables);
+  ScanStoreDir(mRootStoreDirectory, foundTables);
 
   for (uint32_t i = 0; i < foundTables.Length(); i++) {
     nsCString table(foundTables[i]);
-    HashStore store(table, GetProvider(table), mRootStoreDirectory);
 
-    nsresult rv = store.Open();
-    if (NS_FAILED(rv))
-      continue;
-
-    LookupCache *lookupCache = GetLookupCache(store.TableName());
+    LookupCache *lookupCache = GetLookupCache(table);
     if (!lookupCache) {
       continue;
     }
 
-    if (!lookupCache->IsPrimed())
+    if (!lookupCache->IsPrimed()) {
       continue;
+    }
 
-    const ChunkSet &adds = store.AddChunks();
-    const ChunkSet &subs = store.SubChunks();
+    if (LookupCache::Cast<LookupCacheV4>(lookupCache)) {
+      LOG(("Active v4 table: %s", table.get()));
+    } else {
+      HashStore store(table, GetProvider(table), mRootStoreDirectory);
 
-    if (adds.Length() == 0 && subs.Length() == 0)
-      continue;
+      nsresult rv = store.Open();
+      if (NS_FAILED(rv)) {
+        continue;
+      }
+
+      const ChunkSet &adds = store.AddChunks();
+      const ChunkSet &subs = store.SubChunks();
 
-    LOG(("Active table: %s", store.TableName().get()));
-    mActiveTablesCache.AppendElement(store.TableName());
+      if (adds.Length() == 0 && subs.Length() == 0) {
+        continue;
+      }
+
+      LOG(("Active v2 table: %s", store.TableName().get()));
+    }
+
+    mActiveTablesCache.AppendElement(table);
   }
 
   return NS_OK;
 }
 
 nsresult
-Classifier::ScanStoreDir(nsTArray<nsCString>& aTables)
+Classifier::ScanStoreDir(nsIFile* aDirectory, nsTArray<nsCString>& aTables)
 {
   nsCOMPtr<nsISimpleEnumerator> entries;
-  nsresult rv = mRootStoreDirectory->GetDirectoryEntries(getter_AddRefs(entries));
+  nsresult rv = aDirectory->GetDirectoryEntries(getter_AddRefs(entries));
   NS_ENSURE_SUCCESS(rv, rv);
 
   bool hasMore;
   while (NS_SUCCEEDED(rv = entries->HasMoreElements(&hasMore)) && hasMore) {
     nsCOMPtr<nsISupports> supports;
     rv = entries->GetNext(getter_AddRefs(supports));
     NS_ENSURE_SUCCESS(rv, rv);
 
     nsCOMPtr<nsIFile> file = do_QueryInterface(supports);
 
+    // If |file| is a directory, recurse to find its entries as well.
+    bool isDirectory;
+    if (NS_FAILED(file->IsDirectory(&isDirectory))) {
+      continue;
+    }
+    if (isDirectory) {
+      ScanStoreDir(file, aTables);
+      continue;
+    }
+
     nsCString leafName;
     rv = file->GetNativeLeafName(leafName);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    nsCString suffix(NS_LITERAL_CSTRING(".sbstore"));
+    // Both v2 and v4 contain .pset file
+    nsCString suffix(NS_LITERAL_CSTRING(".pset"));
 
     int32_t dot = leafName.RFind(suffix, 0);
     if (dot != -1) {
       leafName.Cut(dot, suffix.Length());
       aTables.AppendElement(leafName);
     }
   }
   NS_ENSURE_SUCCESS(rv, rv);

--- a/toolkit/components/url-classifier/Classifier.h
+++ b/toolkit/components/url-classifier/Classifier.h
@@ -147,17 +147,17 @@ private:
   // and on-disk data.
   void RemoveUpdateIntermediaries();
 
 #ifdef MOZ_SAFEBROWSING_DUMP_FAILED_UPDATES
   already_AddRefed<nsIFile> GetFailedUpdateDirectroy();
   nsresult DumpFailedUpdate();
 #endif
 
-  nsresult ScanStoreDir(nsTArray<nsCString>& aTables);
+  nsresult ScanStoreDir(nsIFile* aDirectory, nsTArray<nsCString>& aTables);
 
   nsresult UpdateHashStore(nsTArray<TableUpdate*>* aUpdates,
                            const nsACString& aTable);
 
   nsresult UpdateTableV4(nsTArray<TableUpdate*>* aUpdates,
                          const nsACString& aTable);
 
   nsresult UpdateCache(TableUpdate* aUpdates);