diff --git a/testing/firefox-ui/tests/functional/security/test_safe_browsing_initial_download.py b/testing/firefox-ui/tests/functional/security/test_safe_browsing_initial_download.py
index 80d3493e9b26..385b8f398983 100644
--- a/testing/firefox-ui/tests/functional/security/test_safe_browsing_initial_download.py
+++ b/testing/firefox-ui/tests/functional/security/test_safe_browsing_initial_download.py
@@ -14,24 +14,18 @@ class TestSafeBrowsingInitialDownload(FirefoxTestCase):
             'platforms': ['linux', 'windows_nt', 'darwin'],
             'files': [
                 # Phishing
-                "goog-badbinurl-shavar.cache",
                 "goog-badbinurl-shavar.pset",
                 "goog-badbinurl-shavar.sbstore",
-                "goog-malware-shavar.cache",
                 "goog-malware-shavar.pset",
                 "goog-malware-shavar.sbstore",
-                "goog-phish-shavar.cache",
                 "goog-phish-shavar.pset",
                 "goog-phish-shavar.sbstore",
-                "goog-unwanted-shavar.cache",
                 "goog-unwanted-shavar.pset",
                 "goog-unwanted-shavar.sbstore",
 
                 # Tracking Protections
-                "base-track-digest256.cache",
                 "base-track-digest256.pset",
                 "base-track-digest256.sbstore",
-                "mozstd-trackwhite-digest256.cache",
                 "mozstd-trackwhite-digest256.pset",
                 "mozstd-trackwhite-digest256.sbstore"
                 ]
@@ -39,7 +33,6 @@ class TestSafeBrowsingInitialDownload(FirefoxTestCase):
         {
             'platforms': ['windows_nt'],
             'files': [
-                "goog-downloadwhite-digest256.cache",
                 "goog-downloadwhite-digest256.pset",
                 "goog-downloadwhite-digest256.sbstore"
             ]
diff --git a/toolkit/components/url-classifier/Classifier.cpp b/toolkit/components/url-classifier/Classifier.cpp
index 6b6afd5348f4..e3654d163fef 100644
--- a/toolkit/components/url-classifier/Classifier.cpp
+++ b/toolkit/components/url-classifier/Classifier.cpp
@@ -304,11 +304,11 @@ Classifier::ApplyUpdates(nsTArray<TableUpdate*>* aUpdates)
   LOG(("Applying %d table updates.", aUpdates->Length()));
 
   for (uint32_t i = 0; i < aUpdates->Length(); i++) {
-    // Previous ApplyTableUpdates() may have consumed this update..
+    // Previous UpdateHashStore() may have consumed this update..
     if ((*aUpdates)[i]) {
       // Run all updates for one table
       nsCString updateTable(aUpdates->ElementAt(i)->TableName());
-      rv = ApplyTableUpdates(aUpdates, updateTable);
+      rv = UpdateHashStore(aUpdates, updateTable);
       if (NS_FAILED(rv)) {
         if (rv != NS_ERROR_OUT_OF_MEMORY) {
           Reset();
@@ -344,6 +344,25 @@ Classifier::ApplyUpdates(nsTArray<TableUpdate*>* aUpdates)
   return NS_OK;
 }
 
+nsresult
+Classifier::ApplyFullHashes(nsTArray<TableUpdate*>* aUpdates)
+{
+  LOG(("Applying %d table gethashes.", aUpdates->Length()));
+
+  for (uint32_t i = 0; i < aUpdates->Length(); i++) {
+    TableUpdate *update = aUpdates->ElementAt(i);
+
+    nsresult rv = UpdateCache(update);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    aUpdates->ElementAt(i) = nullptr;
+    delete update;
+  }
+  aUpdates->Clear();
+
+  return NS_OK;
+}
+
 nsresult
 Classifier::MarkSpoiled(nsTArray<nsCString>& aTables)
 {
@@ -354,12 +373,20 @@ Classifier::MarkSpoiled(nsTArray<nsCString>& aTables)
     // Remove any cached Completes for this table
     LookupCache *cache = GetLookupCache(aTables[i]);
     if (cache) {
-      cache->ClearCompleteCache();
+      cache->ClearCache();
     }
   }
   return NS_OK;
 }
 
+int64_t
+Classifier::GetLastUpdateTime(const nsACString& aTableName)
+{
+  int64_t age;
+  bool found = mTableFreshness.Get(aTableName, &age);
+  return found ? (age * PR_MSEC_PER_SEC) : 0;
+}
+
 void
 Classifier::SetLastUpdateTime(const nsACString &aTable,
                               uint64_t updateTime)
@@ -550,24 +577,17 @@ Classifier::RecoverBackups()
   return NS_OK;
 }
 
-/*
- * This will consume+delete updates from the passed nsTArray.
-*/
-nsresult
-Classifier::ApplyTableUpdates(nsTArray<TableUpdate*>* aUpdates,
-                              const nsACString& aTable)
+bool
+Classifier::CheckValidUpdate(nsTArray<TableUpdate*>* aUpdates,
+                             const nsACString& aTable)
 {
-  LOG(("Classifier::ApplyTableUpdates(%s)", PromiseFlatCString(aTable).get()));
-
-  HashStore store(aTable, mStoreDirectory);
-
   // take the quick exit if there is no valid update for us
   // (common case)
   uint32_t validupdates = 0;
 
   for (uint32_t i = 0; i < aUpdates->Length(); i++) {
     TableUpdate *update = aUpdates->ElementAt(i);
-    if (!update || !update->TableName().Equals(store.TableName()))
+    if (!update || !update->TableName().Equals(aTable))
       continue;
     if (update->Empty()) {
       aUpdates->ElementAt(i) = nullptr;
@@ -579,6 +599,24 @@ Classifier::ApplyTableUpdates(nsTArray<TableUpdate*>* aUpdates,
 
   if (!validupdates) {
     // This can happen if the update was only valid for one table.
+    return false;
+  }
+
+  return true;
+}
+
+/*
+ * This will consume+delete updates from the passed nsTArray.
+*/
+nsresult
+Classifier::UpdateHashStore(nsTArray<TableUpdate*>* aUpdates,
+                            const nsACString& aTable)
+{
+  LOG(("Classifier::UpdateHashStore(%s)", PromiseFlatCString(aTable).get()));
+
+  HashStore store(aTable, mStoreDirectory);
+
+  if (!CheckValidUpdate(aUpdates, store.TableName())) {
     return NS_OK;
   }
 
@@ -588,20 +626,22 @@ Classifier::ApplyTableUpdates(nsTArray<TableUpdate*>* aUpdates,
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Read the part of the store that is (only) in the cache
-  LookupCache *prefixSet = GetLookupCache(store.TableName());
-  if (!prefixSet) {
+  LookupCache *lookupCache = GetLookupCache(store.TableName());
+  if (!lookupCache) {
     return NS_ERROR_FAILURE;
   }
+
+  // Clear cache when update
+  lookupCache->ClearCache();
+
   FallibleTArray<uint32_t> AddPrefixHashes;
-  rv = prefixSet->GetPrefixes(AddPrefixHashes);
+  rv = lookupCache->GetPrefixes(AddPrefixHashes);
   NS_ENSURE_SUCCESS(rv, rv);
   rv = store.AugmentAdds(AddPrefixHashes);
   NS_ENSURE_SUCCESS(rv, rv);
   AddPrefixHashes.Clear();
 
   uint32_t applied = 0;
-  bool updateFreshness = false;
-  bool hasCompletes = false;
 
   for (uint32_t i = 0; i < aUpdates->Length(); i++) {
     TableUpdate *update = aUpdates->ElementAt(i);
@@ -623,17 +663,6 @@ Classifier::ApplyTableUpdates(nsTArray<TableUpdate*>* aUpdates,
     LOG(("  %d add expirations", update->AddExpirations().Length()));
     LOG(("  %d sub expirations", update->SubExpirations().Length()));
 
-    if (!update->IsLocalUpdate()) {
-      updateFreshness = true;
-      LOG(("Remote update, updating freshness"));
-    }
-
-    if (update->AddCompletes().Length() > 0
-        || update->SubCompletes().Length() > 0) {
-      hasCompletes = true;
-      LOG(("Contains Completes, keeping cache."));
-    }
-
     aUpdates->ElementAt(i) = nullptr;
     delete update;
   }
@@ -643,11 +672,6 @@ Classifier::ApplyTableUpdates(nsTArray<TableUpdate*>* aUpdates,
   rv = store.Rebuild();
   NS_ENSURE_SUCCESS(rv, rv);
 
-  // Not an update with Completes, clear all completes data.
-  if (!hasCompletes) {
-    store.ClearCompletes();
-  }
-
   LOG(("Table %s now has:", store.TableName().get()));
   LOG(("  %d add chunks", store.AddChunks().Length()));
   LOG(("  %d add prefixes", store.AddPrefixes().Length()));
@@ -661,21 +685,41 @@ Classifier::ApplyTableUpdates(nsTArray<TableUpdate*>* aUpdates,
 
   // At this point the store is updated and written out to disk, but
   // the data is still in memory.  Build our quick-lookup table here.
-  rv = prefixSet->Build(store.AddPrefixes(), store.AddCompletes());
+  rv = lookupCache->Build(store.AddPrefixes(), store.AddCompletes());
   NS_ENSURE_SUCCESS(rv, rv);
 
 #if defined(DEBUG)
-  prefixSet->Dump();
+  lookupCache->Dump();
 #endif
-  rv = prefixSet->WriteFile();
+  rv = lookupCache->WriteFile();
   NS_ENSURE_SUCCESS(rv, rv);
 
-  if (updateFreshness) {
-    int64_t now = (PR_Now() / PR_USEC_PER_SEC);
-    LOG(("Successfully updated %s", store.TableName().get()));
-    mTableFreshness.Put(store.TableName(), now);
+  int64_t now = (PR_Now() / PR_USEC_PER_SEC);
+  LOG(("Successfully updated %s", store.TableName().get()));
+  mTableFreshness.Put(store.TableName(), now);
+
+  return NS_OK;
+}
+
+nsresult
+Classifier::UpdateCache(TableUpdate* aUpdate)
+{
+  if (!aUpdate) {
+    return NS_OK;
   }
 
+  nsAutoCString table(aUpdate->TableName());
+  LOG(("Classifier::UpdateCache(%s)", table.get()));
+
+  LookupCache *lookupCache = GetLookupCache(table);
+  NS_ENSURE_TRUE(lookupCache, NS_ERROR_FAILURE);
+
+  lookupCache->AddCompletionsToCache(aUpdate->AddCompletes());
+
+#if defined(DEBUG)
+  lookupCache->DumpCache();
+#endif
+
   return NS_OK;
 }
 
diff --git a/toolkit/components/url-classifier/Classifier.h b/toolkit/components/url-classifier/Classifier.h
index 6b5930982ce8..d40c4ad8b3a8 100644
--- a/toolkit/components/url-classifier/Classifier.h
+++ b/toolkit/components/url-classifier/Classifier.h
@@ -55,12 +55,19 @@ public:
    * the updates in the array and clears it.  Wacky!
    */
   nsresult ApplyUpdates(nsTArray<TableUpdate*>* aUpdates);
+
+  /**
+   * Apply full hashes retrived from gethash to cache.
+   */
+  nsresult ApplyFullHashes(nsTArray<TableUpdate*>* aUpdates);
+
   /**
    * Failed update. Spoil the entries so we don't block hosts
    * unnecessarily
    */
   nsresult MarkSpoiled(nsTArray<nsCString>& aTables);
   void SetLastUpdateTime(const nsACString& aTableName, uint64_t updateTime);
+  int64_t GetLastUpdateTime(const nsACString& aTableName);
   nsresult CacheCompletions(const CacheResultArray& aResults);
   uint32_t GetHashKey(void) { return mHashKey; }
   /*
@@ -84,11 +91,16 @@ private:
   nsresult RegenActiveTables();
   nsresult ScanStoreDir(nsTArray<nsCString>& aTables);
 
-  nsresult ApplyTableUpdates(nsTArray<TableUpdate*>* aUpdates,
-                             const nsACString& aTable);
+  nsresult UpdateHashStore(nsTArray<TableUpdate*>* aUpdates,
+                           const nsACString& aTable);
+
+  nsresult UpdateCache(TableUpdate* aUpdates);
 
   LookupCache *GetLookupCache(const nsACString& aTable);
 
+  bool CheckValidUpdate(nsTArray<TableUpdate*>* aUpdates,
+                        const nsACString& aTable);
+
   // Root dir of the Local profile.
   nsCOMPtr<nsIFile> mCacheDirectory;
   // Main directory where to store the databases.
diff --git a/toolkit/components/url-classifier/HashStore.cpp b/toolkit/components/url-classifier/HashStore.cpp
index ed1822d42ec7..3c93a4b2e2f2 100644
--- a/toolkit/components/url-classifier/HashStore.cpp
+++ b/toolkit/components/url-classifier/HashStore.cpp
@@ -165,6 +165,7 @@ HashStore::HashStore(const nsACString& aTableName, nsIFile* aStoreDir)
   : mTableName(aTableName)
   , mStoreDirectory(aStoreDir)
   , mInUpdate(false)
+  , mFileSize(0)
 {
 }
 
@@ -187,13 +188,18 @@ HashStore::Reset()
   rv = storeFile->Remove(false);
   NS_ENSURE_SUCCESS(rv, rv);
 
+  mFileSize = 0;
+
   return NS_OK;
 }
 
 nsresult
-HashStore::CheckChecksum(nsIFile* aStoreFile,
-                         uint32_t aFileSize)
+HashStore::CheckChecksum(uint32_t aFileSize)
 {
+  if (!mInputStream) {
+    return NS_OK;
+  }
+
   // Check for file corruption by
   // comparing the stored checksum to actual checksum of data
   nsAutoCString hash;
@@ -255,11 +261,8 @@ HashStore::Open()
     return NS_ERROR_FAILURE;
   }
 
-  uint32_t fileSize32 = static_cast<uint32_t>(fileSize);
-  mInputStream = NS_BufferInputStream(origStream, fileSize32);
-
-  rv = CheckChecksum(storeFile, fileSize32);
-  SUCCESS_OR_RESET(rv);
+  mFileSize = static_cast<uint32_t>(fileSize);
+  mInputStream = NS_BufferInputStream(origStream, mFileSize);
 
   rv = ReadHeader();
   SUCCESS_OR_RESET(rv);
@@ -267,9 +270,6 @@ HashStore::Open()
   rv = SanityCheck();
   SUCCESS_OR_RESET(rv);
 
-  rv = ReadChunkNumbers();
-  SUCCESS_OR_RESET(rv);
-
   return NS_OK;
 }
 
@@ -363,7 +363,9 @@ HashStore::UpdateHeader()
 nsresult
 HashStore::ReadChunkNumbers()
 {
-  NS_ENSURE_STATE(mInputStream);
+  if (!mInputStream || AlreadyReadChunkNumbers()) {
+    return NS_OK;
+  }
 
   nsCOMPtr<nsISeekableStream> seekable = do_QueryInterface(mInputStream);
   nsresult rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
@@ -403,6 +405,45 @@ HashStore::ReadHashes()
   rv = ReadSubPrefixes();
   NS_ENSURE_SUCCESS(rv, rv);
 
+  // If completions was read before, then we are done here.
+  if (AlreadyReadCompletions()) {
+    return NS_OK;
+  }
+
+  rv = ReadTArray(mInputStream, &mAddCompletes, mHeader.numAddCompletes);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = ReadTArray(mInputStream, &mSubCompletes, mHeader.numSubCompletes);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+
+nsresult
+HashStore::ReadCompletions()
+{
+  if (!mInputStream || AlreadyReadCompletions()) {
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIFile> storeFile;
+  nsresult rv = mStoreDirectory->Clone(getter_AddRefs(storeFile));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = storeFile->AppendNative(mTableName + NS_LITERAL_CSTRING(STORE_SUFFIX));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  uint32_t offset = mFileSize -
+                    sizeof(struct AddComplete) * mHeader.numAddCompletes -
+                    sizeof(struct SubComplete) * mHeader.numSubCompletes -
+                    nsCheckSummedOutputStream::CHECKSUM_SIZE;
+
+  nsCOMPtr<nsISeekableStream> seekable = do_QueryInterface(mInputStream);
+
+  rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET, offset);
+  NS_ENSURE_SUCCESS(rv, rv);
+
   rv = ReadTArray(mInputStream, &mAddCompletes, mHeader.numAddCompletes);
   NS_ENSURE_SUCCESS(rv, rv);
 
@@ -412,12 +453,28 @@ HashStore::ReadHashes()
   return NS_OK;
 }
 
+nsresult
+HashStore::PrepareForUpdate()
+{
+  nsresult rv = CheckChecksum(mFileSize);
+  SUCCESS_OR_RESET(rv);
+
+  rv = ReadChunkNumbers();
+  SUCCESS_OR_RESET(rv);
+
+  rv = ReadHashes();
+  SUCCESS_OR_RESET(rv);
+
+  return NS_OK;
+}
+
 nsresult
 HashStore::BeginUpdate()
 {
-  // Read the rest of the store in memory.
-  nsresult rv = ReadHashes();
-  SUCCESS_OR_RESET(rv);
+  // Check wether the file is corrupted and read the rest of the store
+  // in memory.
+  nsresult rv = PrepareForUpdate();
+  NS_ENSURE_SUCCESS(rv, rv);
 
   // Close input stream, won't be needed any more and
   // we will rewrite ourselves.
@@ -1066,5 +1123,61 @@ HashStore::AugmentAdds(const nsTArray<uint32_t>& aPrefixes)
   return NS_OK;
 }
 
+ChunkSet&
+HashStore::AddChunks()
+{
+  ReadChunkNumbers();
+
+  return mAddChunks;
+}
+
+ChunkSet&
+HashStore::SubChunks()
+{
+  ReadChunkNumbers();
+
+  return mSubChunks;
+}
+
+AddCompleteArray&
+HashStore::AddCompletes()
+{
+  ReadCompletions();
+
+  return mAddCompletes;
+}
+
+SubCompleteArray&
+HashStore::SubCompletes()
+{
+  ReadCompletions();
+
+  return mSubCompletes;
+}
+
+bool
+HashStore::AlreadyReadChunkNumbers()
+{
+  // If there are chunks but chunk set not yet contains any data
+  // Then we haven't read chunk numbers.
+  if ((mHeader.numAddChunks != 0 && mAddChunks.Length() == 0) ||
+      (mHeader.numSubChunks != 0 && mSubChunks.Length() == 0)) {
+    return false;
+  }
+  return true;
+}
+
+bool
+HashStore::AlreadyReadCompletions()
+{
+  // If there are completions but completion set not yet contains any data
+  // Then we haven't read completions.
+  if ((mHeader.numAddCompletes != 0 && mAddCompletes.Length() == 0) ||
+      (mHeader.numSubCompletes != 0 && mSubCompletes.Length() == 0)) {
+    return false;
+  }
+  return true;
+}
+
 } // namespace safebrowsing
 } // namespace mozilla
diff --git a/toolkit/components/url-classifier/HashStore.h b/toolkit/components/url-classifier/HashStore.h
index 70b937d50c5d..7d8c81b151ee 100644
--- a/toolkit/components/url-classifier/HashStore.h
+++ b/toolkit/components/url-classifier/HashStore.h
@@ -23,7 +23,7 @@ namespace safebrowsing {
 class TableUpdate {
 public:
   explicit TableUpdate(const nsACString& aTable)
-      : mTable(aTable), mLocalUpdate(false) {}
+      : mTable(aTable) {}
   const nsCString& TableName() const { return mTable; }
 
   bool Empty() const {
@@ -60,8 +60,6 @@ public:
   MOZ_MUST_USE nsresult NewSubComplete(uint32_t aAddChunk,
                                        const Completion& aCompletion,
                                        uint32_t aSubChunk);
-  void SetLocalUpdate(void) { mLocalUpdate = true; }
-  bool IsLocalUpdate(void) { return mLocalUpdate; }
 
   ChunkSet& AddChunks() { return mAddChunks; }
   ChunkSet& SubChunks() { return mSubChunks; }
@@ -78,8 +76,6 @@ public:
 
 private:
   nsCString mTable;
-  // Update not from the remote server (no freshness)
-  bool mLocalUpdate;
 
   // The list of chunk numbers that we have for each of the type of chunks.
   ChunkSet mAddChunks;
@@ -112,12 +108,12 @@ public:
   // prefixes+chunknumbers dataset.
   nsresult AugmentAdds(const nsTArray<uint32_t>& aPrefixes);
 
-  ChunkSet& AddChunks() { return mAddChunks; }
-  ChunkSet& SubChunks() { return mSubChunks; }
+  ChunkSet& AddChunks();
+  ChunkSet& SubChunks();
   AddPrefixArray& AddPrefixes() { return mAddPrefixes; }
-  AddCompleteArray& AddCompletes() { return mAddCompletes; }
   SubPrefixArray& SubPrefixes() { return mSubPrefixes; }
-  SubCompleteArray& SubCompletes() { return mSubCompletes; }
+  AddCompleteArray& AddCompletes();
+  SubCompleteArray& SubCompletes();
 
   // =======
   // Updates
@@ -149,9 +145,10 @@ private:
   nsresult SanityCheck();
   nsresult CalculateChecksum(nsAutoCString& aChecksum, uint32_t aFileSize,
                              bool aChecksumPresent);
-  nsresult CheckChecksum(nsIFile* aStoreFile, uint32_t aFileSize);
+  nsresult CheckChecksum(uint32_t aFileSize);
   void UpdateHeader();
 
+  nsresult ReadCompletions();
   nsresult ReadChunkNumbers();
   nsresult ReadHashes();
 
@@ -163,6 +160,11 @@ private:
 
   nsresult ProcessSubs();
 
+  nsresult PrepareForUpdate();
+
+  bool AlreadyReadChunkNumbers();
+  bool AlreadyReadCompletions();
+
  // This is used for checking that the database is correct and for figuring out
  // the number of chunks, etc. to read from disk on restart.
   struct Header {
@@ -202,6 +204,8 @@ private:
   // updates from the completion server and updates from the regular server.
   AddCompleteArray mAddCompletes;
   SubCompleteArray mSubCompletes;
+
+  uint32_t mFileSize;
 };
 
 } // namespace safebrowsing
diff --git a/toolkit/components/url-classifier/LookupCache.cpp b/toolkit/components/url-classifier/LookupCache.cpp
index f0220bed9eac..bcceb7e47cae 100644
--- a/toolkit/components/url-classifier/LookupCache.cpp
+++ b/toolkit/components/url-classifier/LookupCache.cpp
@@ -6,7 +6,6 @@
 #include "LookupCache.h"
 #include "HashStore.h"
 #include "nsISeekableStream.h"
-#include "nsISafeOutputStream.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/Logging.h"
 #include "nsNetUtil.h"
@@ -17,19 +16,17 @@
 // The latter solely exists to store the data needed to handle
 // the updates from the protocol.
 
-// This module has its own store, which stores the Completions,
-// mostly caching lookups that have happened over the net.
-// The prefixes are cached/checked by looking them up in the
-// PrefixSet.
+// This module provides a front for PrefixSet, mUpdateCompletions,
+// and mGetHashCache, which together contain everything needed to
+// provide a classification as long as the data is up to date.
 
-// Data format for the ".cache" files:
-//    uint32_t magic           Identify the file type
-//    uint32_t version         Version identifier for file format
-//    uint32_t numCompletions  Amount of completions stored
-//    0...numCompletions     256-bit Completions
-
-// Name of the lookupcomplete cache
-#define CACHE_SUFFIX ".cache"
+// PrefixSet stores and provides lookups for 4-byte prefixes.
+// mUpdateCompletions contains 32-byte completions which were
+// contained in updates. They are retrieved from HashStore/.sbtore
+// on startup.
+// mGetHashCache contains 32-byte completions which were
+// returned from the gethash server. They are not serialized,
+// only cached until the next update.
 
 // Name of the persistent PrefixSet storage
 #define PREFIXSET_SUFFIX  ".pset"
@@ -42,9 +39,6 @@ extern mozilla::LazyLogModule gUrlClassifierDbServiceLog;
 namespace mozilla {
 namespace safebrowsing {
 
-const uint32_t LOOKUPCACHE_MAGIC = 0x1231af3e;
-const uint32_t CURRENT_VERSION = 2;
-
 LookupCache::LookupCache(const nsACString& aTableName, nsIFile* aStoreDir)
   : mPrimed(false)
   , mTableName(aTableName)
@@ -69,40 +63,10 @@ LookupCache::~LookupCache()
 nsresult
 LookupCache::Open()
 {
-  nsCOMPtr<nsIFile> storeFile;
-
-  nsresult rv = mStoreDirectory->Clone(getter_AddRefs(storeFile));
+  LOG(("Reading Completions"));
+  nsresult rv = ReadCompletions();
   NS_ENSURE_SUCCESS(rv, rv);
 
-  rv = storeFile->AppendNative(mTableName + NS_LITERAL_CSTRING(CACHE_SUFFIX));
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  nsCOMPtr<nsIInputStream> inputStream;
-  rv = NS_NewLocalFileInputStream(getter_AddRefs(inputStream), storeFile,
-                                  PR_RDONLY | nsIFile::OS_READAHEAD);
-
-  if (NS_FAILED(rv) && rv != NS_ERROR_FILE_NOT_FOUND) {
-    Reset();
-    return rv;
-  }
-
-  if (rv == NS_ERROR_FILE_NOT_FOUND) {
-    // Simply lacking a .cache file is a recoverable error,
-    // as unlike the .pset/.sbstore files it is a pure cache.
-    // Just create a new empty one.
-    ClearCompleteCache();
-  } else {
-    // Read in the .cache file
-    rv = ReadHeader(inputStream);
-    NS_ENSURE_SUCCESS(rv, rv);
-    LOG(("ReadCompletions"));
-    rv = ReadCompletions(inputStream);
-    NS_ENSURE_SUCCESS(rv, rv);
-
-    rv = inputStream->Close();
-    NS_ENSURE_SUCCESS(rv, rv);
-  }
-
   LOG(("Loading PrefixSet"));
   rv = LoadPrefixSet();
   NS_ENSURE_SUCCESS(rv, rv);
@@ -121,20 +85,13 @@ LookupCache::Reset()
 {
   LOG(("LookupCache resetting"));
 
-  nsCOMPtr<nsIFile> storeFile;
   nsCOMPtr<nsIFile> prefixsetFile;
-  nsresult rv = mStoreDirectory->Clone(getter_AddRefs(storeFile));
-  NS_ENSURE_SUCCESS(rv, rv);
-  rv = mStoreDirectory->Clone(getter_AddRefs(prefixsetFile));
+  nsresult rv = mStoreDirectory->Clone(getter_AddRefs(prefixsetFile));
   NS_ENSURE_SUCCESS(rv, rv);
 
-  rv = storeFile->AppendNative(mTableName + NS_LITERAL_CSTRING(CACHE_SUFFIX));
-  NS_ENSURE_SUCCESS(rv, rv);
   rv = prefixsetFile->AppendNative(mTableName + NS_LITERAL_CSTRING(PREFIXSET_SUFFIX));
   NS_ENSURE_SUCCESS(rv, rv);
 
-  rv = storeFile->Remove(false);
-  NS_ENSURE_SUCCESS(rv, rv);
   rv = prefixsetFile->Remove(false);
   NS_ENSURE_SUCCESS(rv, rv);
 
@@ -151,13 +108,13 @@ LookupCache::Build(AddPrefixArray& aAddPrefixes,
   Telemetry::Accumulate(Telemetry::URLCLASSIFIER_LC_COMPLETIONS,
                         static_cast<uint32_t>(aAddCompletes.Length()));
 
-  mCompletions.Clear();
-  mCompletions.SetCapacity(aAddCompletes.Length());
+  mUpdateCompletions.Clear();
+  mUpdateCompletions.SetCapacity(aAddCompletes.Length());
   for (uint32_t i = 0; i < aAddCompletes.Length(); i++) {
-    mCompletions.AppendElement(aAddCompletes[i].CompleteHash());
+    mUpdateCompletions.AppendElement(aAddCompletes[i].CompleteHash());
   }
   aAddCompletes.Clear();
-  mCompletions.Sort();
+  mUpdateCompletions.Sort();
 
   Telemetry::Accumulate(Telemetry::URLCLASSIFIER_LC_PREFIXES,
                         static_cast<uint32_t>(aAddPrefixes.Length()));
@@ -169,17 +126,43 @@ LookupCache::Build(AddPrefixArray& aAddPrefixes,
   return NS_OK;
 }
 
+nsresult
+LookupCache::AddCompletionsToCache(AddCompleteArray& aAddCompletes)
+{
+  for (uint32_t i = 0; i < aAddCompletes.Length(); i++) {
+    if (mGetHashCache.BinaryIndexOf(aAddCompletes[i].CompleteHash()) == mGetHashCache.NoIndex) {
+      mGetHashCache.AppendElement(aAddCompletes[i].CompleteHash());
+    }
+  }
+  mGetHashCache.Sort();
+
+  return NS_OK;
+}
+
 #if defined(DEBUG)
+void
+LookupCache::DumpCache()
+{
+  if (!LOG_ENABLED())
+    return;
+
+  for (uint32_t i = 0; i < mGetHashCache.Length(); i++) {
+    nsAutoCString str;
+    mGetHashCache[i].ToHexString(str);
+    LOG(("Caches: %s", str.get()));
+  }
+}
+
 void
 LookupCache::Dump()
 {
   if (!LOG_ENABLED())
     return;
 
-  for (uint32_t i = 0; i < mCompletions.Length(); i++) {
+  for (uint32_t i = 0; i < mUpdateCompletions.Length(); i++) {
     nsAutoCString str;
-    mCompletions[i].ToHexString(str);
-    LOG(("Completion: %s", str.get()));
+    mUpdateCompletions[i].ToHexString(str);
+    LOG(("Update: %s", str.get()));
   }
 }
 #endif
@@ -202,7 +185,9 @@ LookupCache::Has(const Completion& aCompletion,
     *aHas = true;
   }
 
-  if (mCompletions.BinaryIndexOf(aCompletion) != nsTArray<Completion>::NoIndex) {
+  // TODO: We may need to distinguish completions found in cache or update in the future
+  if ((mGetHashCache.BinaryIndexOf(aCompletion) != nsTArray<Completion>::NoIndex) ||
+      (mUpdateCompletions.BinaryIndexOf(aCompletion) != nsTArray<Completion>::NoIndex)) {
     LOG(("Complete in %s", mTableName.get()));
     *aComplete = true;
     *aHas = true;
@@ -214,36 +199,8 @@ LookupCache::Has(const Completion& aCompletion,
 nsresult
 LookupCache::WriteFile()
 {
-  nsCOMPtr<nsIFile> storeFile;
-  nsresult rv = mStoreDirectory->Clone(getter_AddRefs(storeFile));
-  NS_ENSURE_SUCCESS(rv, rv);
-  rv = storeFile->AppendNative(mTableName + NS_LITERAL_CSTRING(CACHE_SUFFIX));
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  nsCOMPtr<nsIOutputStream> out;
-  rv = NS_NewSafeLocalFileOutputStream(getter_AddRefs(out), storeFile,
-                                       PR_WRONLY | PR_TRUNCATE | PR_CREATE_FILE);
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  UpdateHeader();
-  LOG(("Writing %d completions", mHeader.numCompletions));
-
-  uint32_t written;
-  rv = out->Write(reinterpret_cast<char*>(&mHeader), sizeof(mHeader), &written);
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  rv = WriteTArray(out, mCompletions);
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  nsCOMPtr<nsISafeOutputStream> safeOut = do_QueryInterface(out);
-  rv = safeOut->Finish();
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  rv = EnsureSizeConsistent();
-  NS_ENSURE_SUCCESS(rv, rv);
-
   nsCOMPtr<nsIFile> psFile;
-  rv = mStoreDirectory->Clone(getter_AddRefs(psFile));
+  nsresult rv = mStoreDirectory->Clone(getter_AddRefs(psFile));
   NS_ENSURE_SUCCESS(rv, rv);
 
   rv = psFile->AppendNative(mTableName + NS_LITERAL_CSTRING(PREFIXSET_SUFFIX));
@@ -258,102 +215,39 @@ LookupCache::WriteFile()
 void
 LookupCache::ClearAll()
 {
-  ClearCompleteCache();
+  ClearCache();
+  ClearUpdatedCompletions();
   mPrefixSet->SetPrefixes(nullptr, 0);
   mPrimed = false;
 }
 
 void
-LookupCache::ClearCompleteCache()
+LookupCache::ClearUpdatedCompletions()
 {
-  mCompletions.Clear();
-  UpdateHeader();
+  mUpdateCompletions.Clear();
 }
 
 void
-LookupCache::UpdateHeader()
+LookupCache::ClearCache()
 {
-  mHeader.magic = LOOKUPCACHE_MAGIC;
-  mHeader.version = CURRENT_VERSION;
-  mHeader.numCompletions = mCompletions.Length();
+  mGetHashCache.Clear();
 }
 
 nsresult
-LookupCache::EnsureSizeConsistent()
+LookupCache::ReadCompletions()
 {
-  nsCOMPtr<nsIFile> storeFile;
-  nsresult rv = mStoreDirectory->Clone(getter_AddRefs(storeFile));
-  NS_ENSURE_SUCCESS(rv, rv);
-  rv = storeFile->AppendNative(mTableName + NS_LITERAL_CSTRING(CACHE_SUFFIX));
+  HashStore store(mTableName, mStoreDirectory);
+
+  nsresult rv = store.Open();
   NS_ENSURE_SUCCESS(rv, rv);
 
-  int64_t fileSize;
-  rv = storeFile->GetFileSize(&fileSize);
-  NS_ENSURE_SUCCESS(rv, rv);
+  mUpdateCompletions.Clear();
 
-  if (fileSize < 0) {
-    return NS_ERROR_FAILURE;
+  const AddCompleteArray& addComplete = store.AddCompletes();
+  for (uint32_t i = 0; i < addComplete.Length(); i++) {
+    mUpdateCompletions.AppendElement(addComplete[i].complete);
   }
 
-  int64_t expectedSize = sizeof(mHeader)
-                        + mHeader.numCompletions*sizeof(Completion);
-  if (expectedSize != fileSize) {
-    NS_WARNING("File length does not match. Probably corrupted.");
-    Reset();
-    return NS_ERROR_FILE_CORRUPTED;
-  }
-
-  return NS_OK;
-}
-
-nsresult
-LookupCache::ReadHeader(nsIInputStream* aInputStream)
-{
-  if (!aInputStream) {
-    ClearCompleteCache();
-    return NS_OK;
-  }
-
-  nsCOMPtr<nsISeekableStream> seekable = do_QueryInterface(aInputStream);
-  nsresult rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET, 0);
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  void *buffer = &mHeader;
-  rv = NS_ReadInputStreamToBuffer(aInputStream,
-                                  &buffer,
-                                  sizeof(Header));
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  if (mHeader.magic != LOOKUPCACHE_MAGIC || mHeader.version != CURRENT_VERSION) {
-    NS_WARNING("Unexpected header data in the store.");
-    Reset();
-    return NS_ERROR_FILE_CORRUPTED;
-  }
-  LOG(("%d completions present", mHeader.numCompletions));
-
-  rv = EnsureSizeConsistent();
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  return NS_OK;
-}
-
-nsresult
-LookupCache::ReadCompletions(nsIInputStream* aInputStream)
-{
-  if (!mHeader.numCompletions) {
-    mCompletions.Clear();
-    return NS_OK;
-  }
-
-  nsCOMPtr<nsISeekableStream> seekable = do_QueryInterface(aInputStream);
-  nsresult rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET, sizeof(Header));
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  rv = ReadTArray(aInputStream, &mCompletions, mHeader.numCompletions);
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  LOG(("Read %d completions", mCompletions.Length()));
-
   return NS_OK;
 }
 
diff --git a/toolkit/components/url-classifier/LookupCache.h b/toolkit/components/url-classifier/LookupCache.h
index 85702a7cb9d1..f66742b474b4 100644
--- a/toolkit/components/url-classifier/LookupCache.h
+++ b/toolkit/components/url-classifier/LookupCache.h
@@ -108,10 +108,13 @@ public:
   // This will Clear() the passed arrays when done.
   nsresult Build(AddPrefixArray& aAddPrefixes,
                  AddCompleteArray& aAddCompletes);
+  nsresult AddCompletionsToCache(AddCompleteArray& aAddCompletes);
   nsresult GetPrefixes(FallibleTArray<uint32_t>& aAddPrefixes);
-  void ClearCompleteCache();
+  void ClearUpdatedCompletions();
+  void ClearCache();
 
 #if DEBUG
+  void DumpCache();
   void Dump();
 #endif
   nsresult WriteFile();
@@ -122,28 +125,22 @@ public:
 private:
   void ClearAll();
   nsresult Reset();
-  void UpdateHeader();
-  nsresult ReadHeader(nsIInputStream* aInputStream);
-  nsresult ReadCompletions(nsIInputStream* aInputStream);
-  nsresult EnsureSizeConsistent();
+  nsresult ReadCompletions();
   nsresult LoadPrefixSet();
+  nsresult LoadCompletions();
   // Construct a Prefix Set with known prefixes.
   // This will Clear() aAddPrefixes when done.
   nsresult ConstructPrefixSet(AddPrefixArray& aAddPrefixes);
 
-  struct Header {
-    uint32_t magic;
-    uint32_t version;
-    uint32_t numCompletions;
-  };
-  Header mHeader;
-
   bool mPrimed;
   nsCString mTableName;
   nsCOMPtr<nsIFile> mStoreDirectory;
-  CompletionArray mCompletions;
   // Set of prefixes known to be in the database
   RefPtr<nsUrlClassifierPrefixSet> mPrefixSet;
+  // Full length hashes obtained in update request
+  CompletionArray mUpdateCompletions;
+  // Full length hashes obtained in gethash request
+  CompletionArray mGetHashCache;
 };
 
 } // namespace safebrowsing
diff --git a/toolkit/components/url-classifier/nsIUrlClassifierDBService.idl b/toolkit/components/url-classifier/nsIUrlClassifierDBService.idl
index ae0c66e86d6a..0c30d85daec9 100644
--- a/toolkit/components/url-classifier/nsIUrlClassifierDBService.idl
+++ b/toolkit/components/url-classifier/nsIUrlClassifierDBService.idl
@@ -191,6 +191,13 @@ interface nsIUrlClassifierDBService : nsISupports
    * database, emptying all tables.  Mostly intended for use in unit tests.
    */
   void resetDatabase();
+
+  /**
+   * Reload he url-classifier database. This will empty all cache for
+   * completions from gethash, and reload it from database. Mostly intended
+   * for use in tests.
+   */
+  void reloadDatabase();
 };
 
 /**
diff --git a/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp b/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
index cf66b75ccb0d..68c9974670f5 100644
--- a/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
+++ b/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
@@ -628,6 +628,38 @@ nsUrlClassifierDBServiceWorker::ResetDatabase()
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsUrlClassifierDBServiceWorker::ReloadDatabase()
+{
+  nsTArray<nsCString> tables;
+  nsTArray<int64_t> lastUpdateTimes;
+  nsresult rv = mClassifier->ActiveTables(tables);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // We need to make sure lastupdatetime is set after reload database
+  // Otherwise request will be skipped if it is not confirmed.
+  for (uint32_t table = 0; table < tables.Length(); table++) {
+    lastUpdateTimes.AppendElement(mClassifier->GetLastUpdateTime(tables[table]));
+  }
+
+  // This will null out mClassifier
+  rv = CloseDb();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Create new mClassifier and load prefixset and completions from disk.
+  rv = OpenDb();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  for (uint32_t table = 0; table < tables.Length(); table++) {
+    int64_t time = lastUpdateTimes[table];
+    if (time) {
+      mClassifier->SetLastUpdateTime(tables[table], lastUpdateTimes[table]);
+    }
+  }
+
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsUrlClassifierDBServiceWorker::CancelUpdate()
 {
@@ -721,7 +753,6 @@ nsUrlClassifierDBServiceWorker::CacheCompletions(CacheResultArray *results)
       if (NS_FAILED(rv)) {
         return rv;
       }
-      tu->SetLocalUpdate();
       updates.AppendElement(tu);
       pParse->ForgetTableUpdates();
     } else {
@@ -729,7 +760,7 @@ nsUrlClassifierDBServiceWorker::CacheCompletions(CacheResultArray *results)
     }
    }
 
-  mClassifier->ApplyUpdates(&updates);
+  mClassifier->ApplyFullHashes(&updates);
   mLastResults = *resultsPtr;
   return NS_OK;
 }
@@ -1591,6 +1622,14 @@ nsUrlClassifierDBService::ResetDatabase()
   return mWorkerProxy->ResetDatabase();
 }
 
+NS_IMETHODIMP
+nsUrlClassifierDBService::ReloadDatabase()
+{
+  NS_ENSURE_TRUE(gDbBackgroundThread, NS_ERROR_NOT_INITIALIZED);
+
+  return mWorkerProxy->ReloadDatabase();
+}
+
 nsresult
 nsUrlClassifierDBService::CacheCompletions(CacheResultArray *results)
 {
diff --git a/toolkit/components/url-classifier/nsUrlClassifierProxies.cpp b/toolkit/components/url-classifier/nsUrlClassifierProxies.cpp
index f0be4f2000c0..cabe105e8049 100644
--- a/toolkit/components/url-classifier/nsUrlClassifierProxies.cpp
+++ b/toolkit/components/url-classifier/nsUrlClassifierProxies.cpp
@@ -171,6 +171,15 @@ UrlClassifierDBServiceWorkerProxy::ResetDatabase()
   return DispatchToWorkerThread(r);
 }
 
+NS_IMETHODIMP
+UrlClassifierDBServiceWorkerProxy::ReloadDatabase()
+{
+  nsCOMPtr<nsIRunnable> r =
+    NewRunnableMethod(mTarget,
+                      &nsIUrlClassifierDBServiceWorker::ReloadDatabase);
+  return DispatchToWorkerThread(r);
+}
+
 NS_IMETHODIMP
 UrlClassifierDBServiceWorkerProxy::OpenDb()
 {
diff --git a/toolkit/components/url-classifier/tests/mochitest/classifierCommon.js b/toolkit/components/url-classifier/tests/mochitest/classifierCommon.js
index fc21252eb641..04038b6d0f67 100644
--- a/toolkit/components/url-classifier/tests/mochitest/classifierCommon.js
+++ b/toolkit/components/url-classifier/tests/mochitest/classifierCommon.js
@@ -3,6 +3,9 @@
 
 const { classes: Cc, interfaces: Ci, results: Cr } = Components;
 
+var dbService = Cc["@mozilla.org/url-classifier/dbservice;1"]
+                .getService(Ci.nsIUrlClassifierDBService);
+
 function setTimeout(callback, delay) {
   let timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
   timer.initWithCallback({ notify: callback },
@@ -11,8 +14,6 @@ function setTimeout(callback, delay) {
 }
 
 function doUpdate(update) {
-  const { classes: Cc, interfaces: Ci, results: Cr } = Components;
-
   let listener = {
     QueryInterface: function(iid)
     {
@@ -48,6 +49,63 @@ function doUpdate(update) {
   }
 }
 
+function doReload() {
+  dbService.reloadDatabase();
+
+  sendAsyncMessage("reloadSuccess");
+}
+
+// SafeBrowsing.jsm is initialized after mozEntries are added. Add observer
+// to receive "finished" event. For the case when this function is called
+// after the event had already been notified, we lookup entries to see if
+// they are already added to database.
+function waitForInit() {
+  let observerService = Cc["@mozilla.org/observer-service;1"]
+                        .getService(Ci.nsIObserverService);
+
+  observerService.addObserver(function() {
+    sendAsyncMessage("safeBrowsingInited");
+  }, "mozentries-update-finished", false);
+
+  // This url must sync with the table, url in SafeBrowsing.jsm addMozEntries
+  const table = "test-phish-simple";
+  const url = "http://itisatrap.org/firefox/its-a-trap.html";
+
+  let secMan = Cc["@mozilla.org/scriptsecuritymanager;1"]
+               .getService(Ci.nsIScriptSecurityManager);
+  let iosvc = Cc["@mozilla.org/network/io-service;1"]
+              .getService(Ci.nsIIOService);
+
+  let principal = secMan.createCodebasePrincipal(
+    iosvc.newURI(url, null, null), {});
+
+  let listener = {
+    QueryInterface: function(iid)
+    {
+      if (iid.equals(Ci.nsISupports) ||
+        iid.equals(Ci.nsIUrlClassifierUpdateObserver))
+        return this;
+      throw Cr.NS_ERROR_NO_INTERFACE;
+    },
+
+    handleEvent: function(value)
+    {
+      if (value === table) {
+        sendAsyncMessage("safeBrowsingInited");
+      }
+    },
+  };
+  dbService.lookup(principal, table, listener);
+}
+
 addMessageListener("doUpdate", ({ testUpdate }) => {
   doUpdate(testUpdate);
 });
+
+addMessageListener("doReload", () => {
+  doReload();
+});
+
+addMessageListener("waitForInit", () => {
+  waitForInit();
+});
diff --git a/toolkit/components/url-classifier/tests/mochitest/classifierHelper.js b/toolkit/components/url-classifier/tests/mochitest/classifierHelper.js
index b70539838802..973f0c2c4d32 100644
--- a/toolkit/components/url-classifier/tests/mochitest/classifierHelper.js
+++ b/toolkit/components/url-classifier/tests/mochitest/classifierHelper.js
@@ -23,6 +23,17 @@ classifierHelper._updates = [];
 // removed after test complete.
 classifierHelper._updatesToCleanup = [];
 
+classifierHelper._initsCB = [];
+
+// This function return a Promise, promise is resolved when SafeBrowsing.jsm
+// is initialized.
+classifierHelper.waitForInit = function() {
+  return new Promise(function(resolve, reject) {
+    classifierHelper._initsCB.push(resolve);
+    gScript.sendAsyncMessage("waitForInit");
+  });
+}
+
 // This function is used to allow completion for specific "list",
 // some lists like "test-malware-simple" is default disabled to ask for complete.
 // "list" is the db we would like to allow it
@@ -115,6 +126,17 @@ classifierHelper.resetDB = function() {
   });
 };
 
+classifierHelper.reloadDatabase = function() {
+  return new Promise(function(resolve, reject) {
+    gScript.addMessageListener("reloadSuccess", function handler() {
+      gScript.removeMessageListener('reloadSuccess', handler);
+      resolve();
+    });
+
+    gScript.sendAsyncMessage("doReload");
+  });
+}
+
 classifierHelper._update = function(testUpdate, onsuccess, onerror) {
   // Queue the task if there is still an on-going update
   classifierHelper._updates.push({"data": testUpdate,
@@ -147,9 +169,17 @@ classifierHelper._updateError = function(errorCode) {
   }
 };
 
+classifierHelper._inited = function() {
+  classifierHelper._initsCB.forEach(function (cb) {
+    cb();
+  });
+  classifierHelper._initsCB = [];
+};
+
 classifierHelper._setup = function() {
   gScript.addMessageListener("updateSuccess", classifierHelper._updateSuccess);
   gScript.addMessageListener("updateError", classifierHelper._updateError);
+  gScript.addMessageListener("safeBrowsingInited", classifierHelper._inited);
 
   // cleanup will be called at end of each testcase to remove all the urls added to database.
   SimpleTest.registerCleanupFunction(classifierHelper._cleanup);
diff --git a/toolkit/components/url-classifier/tests/mochitest/gethash.sjs b/toolkit/components/url-classifier/tests/mochitest/gethash.sjs
index 47f409bd5b8e..9dcc6e0d578f 100644
--- a/toolkit/components/url-classifier/tests/mochitest/gethash.sjs
+++ b/toolkit/components/url-classifier/tests/mochitest/gethash.sjs
@@ -11,6 +11,8 @@ function handleRequest(request, response)
     query[val.slice(0, idx)] = unescape(val.slice(idx + 1));
   });
 
+  var responseBody;
+
   // Store fullhash in the server side.
   if ("list" in query && "fullhash" in query) {
     // In the server side we will store:
@@ -31,18 +33,27 @@ function handleRequest(request, response)
     }
 
     return;
+  // gethash count return how many gethash request received.
+  // This is used by client to know if a gethash request is triggered by gecko
+  } else if ("gethashcount" == request.queryString) {
+    var counter = getState("counter");
+    responseBody = counter == "" ? "0" : counter;
+  } else {
+    var body = new BinaryInputStream(request.bodyInputStream);
+    var avail;
+    var bytes = [];
+
+    while ((avail = body.available()) > 0) {
+      Array.prototype.push.apply(bytes, body.readByteArray(avail));
+    }
+
+    var counter = getState("counter");
+    counter = counter == "" ? "1" : (parseInt(counter) + 1).toString();
+    setState("counter", counter);
+
+    responseBody = parseV2Request(bytes);
   }
 
-  var body = new BinaryInputStream(request.bodyInputStream);
-  var avail;
-  var bytes = [];
-
-  while ((avail = body.available()) > 0) {
-    Array.prototype.push.apply(bytes, body.readByteArray(avail));
-  }
-
-  var responseBody = parseV2Request(bytes);
-
   response.setHeader("Content-Type", "text/plain", false);
   response.write(responseBody);
 
diff --git a/toolkit/components/url-classifier/tests/mochitest/mochitest.ini b/toolkit/components/url-classifier/tests/mochitest/mochitest.ini
index b9c4005911a4..f62089823c67 100644
--- a/toolkit/components/url-classifier/tests/mochitest/mochitest.ini
+++ b/toolkit/components/url-classifier/tests/mochitest/mochitest.ini
@@ -33,3 +33,4 @@ skip-if = (os == 'linux' && debug) #Bug 1199778
 [test_classify_ping.html]
 [test_classify_track.html]
 [test_gethash.html]
+[test_bug1254766.html]
diff --git a/toolkit/components/url-classifier/tests/mochitest/test_bug1254766.html b/toolkit/components/url-classifier/tests/mochitest/test_bug1254766.html
new file mode 100644
index 000000000000..135830b40ca9
--- /dev/null
+++ b/toolkit/components/url-classifier/tests/mochitest/test_bug1254766.html
@@ -0,0 +1,299 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Bug 1272239 - Test gethash.</title>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="classifierHelper.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+
+<script class="testbody" type="text/javascript">
+
+const MALWARE_LIST = "test-malware-simple";
+const MALWARE_HOST1 = "malware.example.com/";
+const MALWARE_HOST2 = "test1.example.com/";
+
+const UNWANTED_LIST = "test-unwanted-simple";
+const UNWANTED_HOST1 = "unwanted.example.com/";
+const UNWANTED_HOST2 = "test2.example.com/";
+
+
+const UNUSED_MALWARE_HOST = "unused.malware.com/";
+const UNUSED_UNWANTED_HOST = "unused.unwanted.com/";
+
+const GETHASH_URL =
+  "http://mochi.test:8888/tests/toolkit/components/url-classifier/tests/mochitest/gethash.sjs";
+
+var gPreGethashCounter = 0;
+var gCurGethashCounter = 0;
+
+var expectLoad = false;
+
+function loadTestFrame() {
+  return new Promise(function(resolve, reject) {
+    var iframe = document.createElement("iframe");
+    iframe.setAttribute("src", "gethashFrame.html");
+    document.body.appendChild(iframe);
+
+    iframe.onload = function() {
+      document.body.removeChild(iframe);
+      resolve();
+    };
+  }).then(getGethashCounter);
+}
+
+function getGethashCounter() {
+  return new Promise(function(resolve, reject) {
+    var xhr = new XMLHttpRequest;
+    xhr.open("PUT", GETHASH_URL + "?gethashcount");
+    xhr.setRequestHeader("Content-Type", "text/plain");
+    xhr.onreadystatechange = function() {
+      if (this.readyState == this.DONE) {
+        gPreGethashCounter = gCurGethashCounter;
+        gCurGethashCounter = parseInt(xhr.response);
+        resolve();
+      }
+    };
+    xhr.send();
+  });
+}
+
+// calculate the fullhash and send it to gethash server
+function addCompletionToServer(list, url) {
+  return new Promise(function(resolve, reject) {
+    var listParam = "list=" + list;
+    var fullhashParam = "fullhash=" + hash(url);
+
+    var xhr = new XMLHttpRequest;
+    xhr.open("PUT", GETHASH_URL + "?" + listParam + "&" + fullhashParam, true);
+    xhr.setRequestHeader("Content-Type", "text/plain");
+    xhr.onreadystatechange = function() {
+      if (this.readyState == this.DONE) {
+        resolve();
+      }
+    };
+    xhr.send();
+  });
+}
+
+function hash(str) {
+  function bytesFromString(str) {
+    var converter =
+      SpecialPowers.Cc["@mozilla.org/intl/scriptableunicodeconverter"]
+                       .createInstance(SpecialPowers.Ci.nsIScriptableUnicodeConverter);
+    converter.charset = "UTF-8";
+    return converter.convertToByteArray(str);
+  }
+
+  var hasher = SpecialPowers.Cc["@mozilla.org/security/hash;1"]
+                               .createInstance(SpecialPowers.Ci.nsICryptoHash);
+
+  var data = bytesFromString(str);
+  hasher.init(hasher.SHA256);
+  hasher.update(data, data.length);
+
+  return hasher.finish(true);
+}
+
+// setup function allows classifier send gethash request for test database
+// also it calculate to fullhash for url and store those hashes in gethash sjs.
+function setup() {
+  classifierHelper.allowCompletion([MALWARE_LIST, UNWANTED_LIST], GETHASH_URL);
+
+  return Promise.all([
+    addCompletionToServer(MALWARE_LIST, MALWARE_HOST1),
+    addCompletionToServer(MALWARE_LIST, MALWARE_HOST2),
+    addCompletionToServer(UNWANTED_LIST, UNWANTED_HOST1),
+    addCompletionToServer(UNWANTED_LIST, UNWANTED_HOST2),
+  ]);
+}
+
+// Reset function in helper try to simulate the behavior we restart firefox
+function reset() {
+  return classifierHelper.resetDB()
+    .catch(err => {
+      ok(false, "Couldn't update classifier. Error code: " + errorCode);
+      // Abort test.
+      SimpleTest.finish();
+    });
+}
+
+function updateUnusedUrl() {
+  var testData  = [
+    { url: UNUSED_MALWARE_HOST,  db: MALWARE_LIST },
+    { url: UNUSED_UNWANTED_HOST, db: UNWANTED_LIST }
+  ];
+
+  return classifierHelper.addUrlToDB(testData)
+    .catch(err => {
+      ok(false, "Couldn't update classifier. Error code: " + err);
+      // Abort test.
+      SimpleTest.finish();
+    });
+}
+
+function addPrefixToDB() {
+  return update(true);
+}
+
+function addCompletionToDB() {
+  return update(false);
+}
+
+function update(prefix = false) {
+  var length = prefix ? 4 : 32;
+  var testData  = [
+    { url: MALWARE_HOST1,  db: MALWARE_LIST,  len: length },
+    { url: MALWARE_HOST2,  db: MALWARE_LIST,  len: length },
+    { url: UNWANTED_HOST1, db: UNWANTED_LIST, len: length },
+    { url: UNWANTED_HOST2, db: UNWANTED_LIST, len: length }
+  ];
+
+  return classifierHelper.addUrlToDB(testData)
+    .catch(err => {
+      ok(false, "Couldn't update classifier. Error code: " + errorCode);
+      // Abort test.
+      SimpleTest.finish();
+    });
+}
+
+// This testcase is to make sure gethash works:
+// 1. Add prefixes to DB.
+// 2. Load test frame contains malware & unwanted url, those urls should be blocked.
+// 3. The second step should also trigger a gethash request since completions is not in
+//    either cache or DB.
+// 4. Load test frame again, since completions is stored in cache now, no gethash
+//    request should be triggered.
+function testGethash() {
+  return Promise.resolve()
+    .then(addPrefixToDB)
+    .then(loadTestFrame)
+    .then(() => {
+       ok(gCurGethashCounter > gPreGethashCounter, "Gethash request is triggered."); })
+    .then(loadTestFrame)
+    .then(() => {
+      ok(gCurGethashCounter == gPreGethashCounter, "Gethash request is not triggered."); })
+    .then(reset);
+}
+
+// This testcase is to make sure an update request will clear completion cache:
+// 1. Add prefixes to DB.
+// 2. Load test frame, this should trigger a gethash request
+// 3. Trigger an update, completion cache should be cleared now.
+// 4. Load test frame again, since cache is cleared now, gethash request should be triggered.
+function testUpdateClearCache() {
+  return Promise.resolve()
+    .then(addPrefixToDB)
+    .then(loadTestFrame)
+    .then(() => {
+      ok(gCurGethashCounter > gPreGethashCounter, "Gethash request is triggered."); })
+    .then(updateUnusedUrl)
+    .then(loadTestFrame)
+    .then(() => {
+      ok(gCurGethashCounter > gPreGethashCounter, "Gethash request is triggered."); })
+    .then(reset);
+}
+
+// This testcae is to make sure completions in update works:
+// 1. Add completions to DB.
+// 2. Load test frame, since completions is stored in DB, gethash request should
+//    not be triggered.
+function testUpdate() {
+  return Promise.resolve()
+    .then(addCompletionToDB)
+    .then(loadTestFrame)
+    .then(() => {
+      ok(gCurGethashCounter == gPreGethashCounter, "Gethash request is not triggered."); })
+    .then(reset);
+}
+
+// This testcase is to make sure an update request will not clear completions in DB:
+// 1. Add completions to DB.
+// 2. Load test frame to make sure completions is stored in database, in this case, gethash
+//    should not be triggered.
+// 3. Trigger an update, cache is cleared, but completions in DB should still remain.
+// 4. Load test frame again, since completions is in DB, gethash request should not be triggered.
+function testUpdateNotClearCompletions() {
+  return Promise.resolve()
+    .then(addCompletionToDB)
+    .then(loadTestFrame)
+    .then(() => {
+      ok(gCurGethashCounter == gPreGethashCounter, "Gethash request is not triggered."); })
+    .then(updateUnusedUrl)
+    .then(loadTestFrame)
+    .then(() => {
+      ok(gCurGethashCounter == gPreGethashCounter, "Gethash request is not triggered."); })
+    .then(reset);
+}
+
+// This testcase is to make sure completion store in DB will properly load after restarting.
+// 1. Add completions to DB.
+// 2. Simulate firefox restart by calling reloadDatabase.
+// 3. Load test frame, since completions should be loaded from DB, no gethash request should
+//    be triggered.
+function testUpdateCompletionsAfterReload() {
+  return Promise.resolve()
+    .then(addCompletionToDB)
+    .then(classifierHelper.reloadDatabase)
+    .then(loadTestFrame)
+    .then(() => {
+      ok(gCurGethashCounter == gPreGethashCounter, "Gethash request is not triggered."); })
+    .then(reset);
+}
+
+// This testcase is to make sure cache will be cleared after restarting
+// 1. Add prefixes to DB.
+// 2. Load test frame, this should trigger a gethash request and completions will be stored in
+//    cache.
+// 3. Load test frame again, no gethash should be triggered because of cache.
+// 4. Simulate firefox restart by calling reloadDatabase.
+// 5. Load test frame again, since cache is cleared, gethash request should be triggered.
+function testGethashCompletionsAfterReload() {
+  return Promise.resolve()
+    .then(addPrefixToDB)
+    .then(loadTestFrame)
+    .then(() => {
+       ok(gCurGethashCounter > gPreGethashCounter, "Gethash request is triggered."); })
+    .then(loadTestFrame)
+    .then(() => {
+      ok(gCurGethashCounter == gPreGethashCounter, "Gethash request is not triggered."); })
+    .then(classifierHelper.reloadDatabase)
+    .then(loadTestFrame)
+    .then(() => {
+       ok(gCurGethashCounter > gPreGethashCounter, "Gethash request is triggered."); })
+    .then(reset);
+}
+
+function runTest() {
+  Promise.resolve()
+    .then(classifierHelper.waitForInit)
+    .then(setup)
+    .then(testGethash)
+    .then(testUpdateClearCache)
+    .then(testUpdate)
+    .then(testUpdateNotClearCompletions)
+    .then(testUpdateCompletionsAfterReload)
+    .then(testGethashCompletionsAfterReload)
+    .then(function() {
+      SimpleTest.finish();
+    }).catch(function(e) {
+      ok(false, "Some test failed with error " + e);
+      SimpleTest.finish();
+    });
+}
+
+SimpleTest.waitForExplicitFinish();
+SpecialPowers.pushPrefEnv({"set": [
+  ["browser.safebrowsing.malware.enabled", true]
+]}, runTest);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/toolkit/components/url-classifier/tests/unit/head_urlclassifier.js b/toolkit/components/url-classifier/tests/unit/head_urlclassifier.js
index 69b3867a3c06..3a72c437a15c 100644
--- a/toolkit/components/url-classifier/tests/unit/head_urlclassifier.js
+++ b/toolkit/components/url-classifier/tests/unit/head_urlclassifier.js
@@ -58,12 +58,6 @@ function cleanUp() {
   delFile("safebrowsing/test-block-simple.sbstore");
   delFile("safebrowsing/test-track-simple.sbstore");
   delFile("safebrowsing/test-trackwhite-simple.sbstore");
-  delFile("safebrowsing/test-phish-simple.cache");
-  delFile("safebrowsing/test-malware-simple.cache");
-  delFile("safebrowsing/test-unwanted-simple.cache");
-  delFile("safebrowsing/test-block-simple.cache");
-  delFile("safebrowsing/test-track-simple.cache");
-  delFile("safebrowsing/test-trackwhite-simple.cache");
   delFile("safebrowsing/test-phish-simple.pset");
   delFile("safebrowsing/test-malware-simple.pset");
   delFile("safebrowsing/test-unwanted-simple.pset");