diff --git a/toolkit/components/url-classifier/Classifier.cpp b/toolkit/components/url-classifier/Classifier.cpp
index 43ed71a4b61e..2adae10967c8 100644
--- a/toolkit/components/url-classifier/Classifier.cpp
+++ b/toolkit/components/url-classifier/Classifier.cpp
@@ -243,14 +243,6 @@ Classifier::Check(const nsACString& aSpec,
     Completion lookupHash;
     lookupHash.FromPlaintext(fragments[i], mCryptoHash);
 
-    // Get list of host keys to look up
-    Completion hostKey;
-    rv = LookupCache::GetKey(fragments[i], &hostKey, mCryptoHash);
-    if (NS_FAILED(rv)) {
-      // Local host on the network.
-      continue;
-    }
-
     if (LOG_ENABLED()) {
       nsAutoCString checking;
       lookupHash.ToHexString(checking);
diff --git a/toolkit/components/url-classifier/LookupCache.cpp b/toolkit/components/url-classifier/LookupCache.cpp
index 1899fe5b916d..7e2c2cf3f0ec 100644
--- a/toolkit/components/url-classifier/LookupCache.cpp
+++ b/toolkit/components/url-classifier/LookupCache.cpp
@@ -372,51 +372,6 @@ LookupCache::IsCanonicalizedIP(const nsACString& aHost)
   return false;
 }
 
-/* static */ nsresult
-LookupCache::GetKey(const nsACString& aSpec,
-                    Completion* aHash,
-                    nsCOMPtr<nsICryptoHash>& aCryptoHash)
-{
-  nsACString::const_iterator begin, end, iter;
-  aSpec.BeginReading(begin);
-  aSpec.EndReading(end);
-
-  iter = begin;
-  if (!FindCharInReadable('/', iter, end)) {
-   return NS_OK;
-  }
-
-  const nsCSubstring& host = Substring(begin, iter);
-
-  if (IsCanonicalizedIP(host)) {
-    nsAutoCString key;
-    key.Assign(host);
-    key.Append('/');
-    return aHash->FromPlaintext(key, aCryptoHash);
-  }
-
-  nsTArray<nsCString> hostComponents;
-  ParseString(PromiseFlatCString(host), '.', hostComponents);
-
-  if (hostComponents.Length() < 2)
-    return NS_ERROR_FAILURE;
-
-  int32_t last = int32_t(hostComponents.Length()) - 1;
-  nsAutoCString lookupHost;
-
-  if (hostComponents.Length() > 2) {
-    lookupHost.Append(hostComponents[last - 2]);
-    lookupHost.Append('.');
-  }
-
-  lookupHost.Append(hostComponents[last - 1]);
-  lookupHost.Append('.');
-  lookupHost.Append(hostComponents[last]);
-  lookupHost.Append('/');
-
-  return aHash->FromPlaintext(lookupHost, aCryptoHash);
-}
-
 /* static */ nsresult
 LookupCache::GetLookupFragments(const nsACString& aSpec,
                                 nsTArray<nsCString>* aFragments)
diff --git a/toolkit/components/url-classifier/LookupCache.h b/toolkit/components/url-classifier/LookupCache.h
index 4e4387bda4e7..885c352e60f0 100644
--- a/toolkit/components/url-classifier/LookupCache.h
+++ b/toolkit/components/url-classifier/LookupCache.h
@@ -24,7 +24,8 @@ namespace safebrowsing {
 
 class LookupResult {
 public:
-  LookupResult() : mComplete(false), mNoise(false), mFresh(false), mProtocolConfirmed(false) {}
+  LookupResult() : mComplete(false), mNoise(false),
+                   mFresh(false), mProtocolConfirmed(false) {}
 
   // The fragment that matched in the LookupCache
   union {
@@ -32,8 +33,13 @@ public:
     Completion complete;
   } hash;
 
-  const Prefix &PrefixHash() { return hash.prefix; }
-  const Completion &CompleteHash() { return hash.complete; }
+  const Prefix &PrefixHash() {
+    return hash.prefix;
+  }
+  const Completion &CompleteHash() {
+    MOZ_ASSERT(!mNoise);
+    return hash.complete;
+  }
 
   bool Confirmed() const { return (mComplete && mFresh) || mProtocolConfirmed; }
   bool Complete() const { return mComplete; }
@@ -42,7 +48,10 @@ public:
   bool mComplete;
 
   // True if this is a noise entry, i.e. an extra entry
-  // that is inserted to mask the true URL we are requesting
+  // that is inserted to mask the true URL we are requesting.
+  // Noise entries will not have a complete 256-bit hash as
+  // they are fetched from the local 32-bit database and we
+  // don't know the corresponding full URL.
   bool mNoise;
 
   // True if we've updated this table recently-enough.
@@ -78,13 +87,6 @@ public:
   //  www.mail.hostname.com/foo/bar -> [hostname.com, mail.hostname.com]
   static nsresult GetHostKeys(const nsACString& aSpec,
                               nsTArray<nsCString>* aHostKeys);
-  // Get the database key for a given URI.  This is the top three
-  // domain components if they exist, otherwise the top two.
-  //  hostname.com/foo/bar -> hostname.com
-  //  mail.hostname.com/foo/bar -> mail.hostname.com
-  //  www.mail.hostname.com/foo/bar -> mail.hostname.com
-  static nsresult GetKey(const nsACString& aSpec, Completion* aHash,
-                         nsCOMPtr<nsICryptoHash>& aCryptoHash);
 
   LookupCache(const nsACString& aTableName, nsIFile* aStoreFile);
   ~LookupCache();
diff --git a/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp b/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
index dedf8fed2b8e..4fa251357d0b 100644
--- a/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
+++ b/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
@@ -705,7 +705,7 @@ nsUrlClassifierDBServiceWorker::CacheMisses(PrefixArray *results)
 
   for (uint32_t i = 0; i < resultsPtr->Length(); i++) {
     mMissCache.AppendElement(resultsPtr->ElementAt(i));
-   }
+  }
   return NS_OK;
 }
 
@@ -914,7 +914,9 @@ nsUrlClassifierLookupCallback::Completion(const nsACString& completeHash,
     LookupResult& result = mResults->ElementAt(i);
 
     // Now, see if it verifies a lookup
-    if (result.CompleteHash() == hash && result.mTableName.Equals(tableName)) {
+    if (!result.mNoise
+        && result.CompleteHash() == hash
+        && result.mTableName.Equals(tableName)) {
       result.mProtocolConfirmed = true;
     }
   }