diff --git a/toolkit/components/url-classifier/Classifier.cpp b/toolkit/components/url-classifier/Classifier.cpp
index 0a71187d529..79604273e59 100644
--- a/toolkit/components/url-classifier/Classifier.cpp
+++ b/toolkit/components/url-classifier/Classifier.cpp
@@ -778,7 +778,7 @@ Classifier::GetLookupCache(const nsACString& aTable)
 nsresult
 Classifier::ReadNoiseEntries(const Prefix& aPrefix,
                              const nsACString& aTableName,
-                             int32_t aCount,
+                             uint32_t aCount,
                              PrefixArray* aNoiseEntries)
 {
   LookupCache *cache = GetLookupCache(aTableName);
diff --git a/toolkit/components/url-classifier/Classifier.h b/toolkit/components/url-classifier/Classifier.h
index fe0cbb906a3..53121bf76c3 100644
--- a/toolkit/components/url-classifier/Classifier.h
+++ b/toolkit/components/url-classifier/Classifier.h
@@ -67,7 +67,7 @@ public:
    */
   nsresult ReadNoiseEntries(const Prefix& aPrefix,
                             const nsACString& aTableName,
-                            int32_t aCount,
+                            uint32_t aCount,
                             PrefixArray* aNoiseEntries);
 private:
   void DropStores();
diff --git a/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp b/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
index 78d1da38f65..8aab9ccab66 100644
--- a/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
+++ b/toolkit/components/url-classifier/nsUrlClassifierDBService.cpp
@@ -116,7 +116,7 @@ public:
   NS_DECL_NSIURLCLASSIFIERDBSERVICE
   NS_DECL_NSIURLCLASSIFIERDBSERVICEWORKER
 
-  nsresult Init(int32_t gethashNoise, nsCOMPtr<nsIFile> aCacheDir,
+  nsresult Init(uint32_t aGethashNoise, nsCOMPtr<nsIFile> aCacheDir,
                 bool aPerClientRandomize);
 
   // Queue a lookup for the worker to perform, called in the main thread.
@@ -150,7 +150,7 @@ private:
 
   nsresult AddNoise(const Prefix aPrefix,
                     const nsCString tableName,
-                    int32_t aCount,
+                    uint32_t aCount,
                     LookupResultArray& results);
 
   nsCOMPtr<nsICryptoHash> mCryptoHash;
@@ -184,7 +184,7 @@ private:
   uint32_t mHashKey;
 
   // The number of noise entries to add to the set of lookup results.
-  int32_t mGethashNoise;
+  uint32_t mGethashNoise;
 
   // Randomize clients with a key or not.
   bool mPerClientRandomize;
@@ -224,11 +224,11 @@ nsUrlClassifierDBServiceWorker::~nsUrlClassifierDBServiceWorker()
 }
 
 nsresult
-nsUrlClassifierDBServiceWorker::Init(int32_t gethashNoise,
+nsUrlClassifierDBServiceWorker::Init(uint32_t aGethashNoise,
                                      nsCOMPtr<nsIFile> aCacheDir,
                                      bool aPerClientRandomize)
 {
-  mGethashNoise = gethashNoise;
+  mGethashNoise = aGethashNoise;
   mCacheDir = aCacheDir;
   mPerClientRandomize = aPerClientRandomize;
 
@@ -357,7 +357,7 @@ nsUrlClassifierDBServiceWorker::HandlePendingLookups()
 nsresult
 nsUrlClassifierDBServiceWorker::AddNoise(const Prefix aPrefix,
                                          const nsCString tableName,
-                                         int32_t aCount,
+                                         uint32_t aCount,
                                          LookupResultArray& results)
 {
   if (aCount < 1) {
@@ -1129,7 +1129,7 @@ nsUrlClassifierDBService::Init()
   // Should we check document loads for malware URIs?
   nsCOMPtr<nsIPrefBranch> prefs = do_GetService(NS_PREFSERVICE_CONTRACTID);
 
-  int32_t gethashNoise = 0;
+  uint32_t gethashNoise = 0;
   if (prefs) {
     bool tmpbool;
     rv = prefs->GetBoolPref(CHECK_MALWARE_PREF, &tmpbool);
@@ -1142,9 +1142,10 @@ nsUrlClassifierDBService::Init()
 
     prefs->AddObserver(CHECK_PHISHING_PREF, this, false);
 
-    if (NS_FAILED(prefs->GetIntPref(GETHASH_NOISE_PREF, &gethashNoise))) {
-      gethashNoise = GETHASH_NOISE_DEFAULT;
-    }
+    int32_t tmpint;
+    rv = prefs->GetIntPref(GETHASH_NOISE_PREF, &tmpint);
+    gethashNoise = (NS_SUCCEEDED(rv) && tmpint >= 0) ?
+      static_cast<uint32_t>(tmpint) : GETHASH_NOISE_DEFAULT;
 
     nsXPIDLCString tmpstr;
     if (NS_SUCCEEDED(prefs->GetCharPref(GETHASH_TABLES_PREF, getter_Copies(tmpstr)))) {
@@ -1153,7 +1154,6 @@ nsUrlClassifierDBService::Init()
 
     prefs->AddObserver(GETHASH_TABLES_PREF, this, false);
 
-    int32_t tmpint;
     rv = prefs->GetIntPref(CONFIRM_AGE_PREF, &tmpint);
     PR_ATOMIC_SET(&gFreshnessGuarantee, NS_SUCCEEDED(rv) ? tmpint : CONFIRM_AGE_DEFAULT_SEC);