diff --git a/toolkit/components/url-classifier/LookupCache.cpp b/toolkit/components/url-classifier/LookupCache.cpp
index 7f86398e1459..9702385b68ab 100644
--- a/toolkit/components/url-classifier/LookupCache.cpp
+++ b/toolkit/components/url-classifier/LookupCache.cpp
@@ -174,9 +174,6 @@ nsresult
 LookupCache::Build(const AddPrefixArray& aAddPrefixes,
                    const AddCompleteArray& aAddCompletes)
 {
-  Telemetry::Accumulate(Telemetry::URLCLASSIFIER_LC_COMPLETIONS,
-                        static_cast<PRUint32>(aAddCompletes.Length()));
-
   mCompletions.Clear();
   mCompletions.SetCapacity(aAddCompletes.Length());
   for (uint32 i = 0; i < aAddCompletes.Length(); i++) {
@@ -184,13 +181,16 @@ LookupCache::Build(const AddPrefixArray& aAddPrefixes,
   }
   mCompletions.Sort();
 
-  Telemetry::Accumulate(Telemetry::URLCLASSIFIER_LC_PREFIXES,
-                        static_cast<PRUint32>(aAddPrefixes.Length()));
+  Telemetry::Accumulate(Telemetry::URLCLASSIFIER_LC_COMPLETIONS,
+                        static_cast<PRUint32>(mCompletions.Length()));
 
   nsresult rv = ConstructPrefixSet(aAddPrefixes);
   NS_ENSURE_SUCCESS(rv, rv);
   mPrimed = true;
 
+  Telemetry::Accumulate(Telemetry::URLCLASSIFIER_LC_PREFIXES,
+                        static_cast<PRUint32>(aAddPrefixes.Length()));
+
   return NS_OK;
 }
 
@@ -683,11 +683,8 @@ LookupCache::ConstructPrefixSet(const AddPrefixArray& aAddPrefixes)
 {
   Telemetry::AutoTimer<Telemetry::URLCLASSIFIER_PS_CONSTRUCT_TIME> timer;
 
-  FallibleTArray<PRUint32> array;
-  nsresult rv = array.SetCapacity(aAddPrefixes.Length());
-  if (NS_FAILED(rv)) {
-    goto error_bailout;
-  }
+  nsTArray<PRUint32> array;
+  array.SetCapacity(aAddPrefixes.Length());
 
   for (uint32 i = 0; i < aAddPrefixes.Length(); i++) {
     array.AppendElement(aAddPrefixes[i].PrefixHash().ToUint32());
@@ -702,7 +699,7 @@ LookupCache::ConstructPrefixSet(const AddPrefixArray& aAddPrefixes)
   array.Sort();
 
   // construct new one, replace old entries
-  rv = mPrefixSet->SetPrefixes(array.Elements(), array.Length());
+  nsresult rv = mPrefixSet->SetPrefixes(array.Elements(), array.Length());
   if (NS_FAILED(rv)) {
     goto error_bailout;
   }