diff --git a/toolkit/components/telemetry/Telemetry.cpp b/toolkit/components/telemetry/Telemetry.cpp
index 3f85d88a18f..f54a379e9e3 100644
--- a/toolkit/components/telemetry/Telemetry.cpp
+++ b/toolkit/components/telemetry/Telemetry.cpp
@@ -60,6 +60,60 @@ namespace {
 using namespace base;
 using namespace mozilla;
 
+template<class EntryType>
+class AutoHashtable : public nsTHashtable<EntryType>
+{
+public:
+  AutoHashtable(PRUint32 initSize = PL_DHASH_MIN_SIZE);
+  ~AutoHashtable();
+  typedef bool (*ReflectEntryFunc)(EntryType *entry, JSContext *cx, JSObject *obj);
+  bool ReflectHashtable(ReflectEntryFunc entryFunc, JSContext *cx, JSObject *obj);
+private:
+  struct EnumeratorArgs {
+    JSContext *cx;
+    JSObject *obj;
+    ReflectEntryFunc entryFunc;
+  };
+  static PLDHashOperator ReflectEntryStub(EntryType *entry, void *arg);
+};
+
+template<class EntryType>
+AutoHashtable<EntryType>::AutoHashtable(PRUint32 initSize)
+{
+  this->Init(initSize);
+}
+
+template<class EntryType>
+AutoHashtable<EntryType>::~AutoHashtable()
+{
+  this->Clear();
+}
+
+template<typename EntryType>
+PLDHashOperator
+AutoHashtable<EntryType>::ReflectEntryStub(EntryType *entry, void *arg)
+{
+  EnumeratorArgs *args = static_cast<EnumeratorArgs *>(arg);
+  if (!args->entryFunc(entry, args->cx, args->obj)) {
+    return PL_DHASH_STOP;
+  }
+  return PL_DHASH_NEXT;
+}
+
+/**
+ * Reflect the individual entries of table into JS, usually by defining
+ * some property and value of obj.  entryFunc is called for each entry.
+ */
+template<typename EntryType>
+bool
+AutoHashtable<EntryType>::ReflectHashtable(ReflectEntryFunc entryFunc,
+                                           JSContext *cx, JSObject *obj)
+{
+  EnumeratorArgs args = { cx, obj, entryFunc };
+  PRUint32 num = EnumerateEntries(ReflectEntryStub, static_cast<void*>(&args));
+  return num == this->Count();
+}
+
 class TelemetryImpl : public nsITelemetry
 {
   NS_DECL_ISUPPORTS
@@ -83,6 +137,8 @@ public:
   typedef nsBaseHashtableET<nsCStringHashKey, StmtStats> SlowSQLEntryType;
 
 private:
+  static bool StatementReflector(SlowSQLEntryType *entry, JSContext *cx,
+                                 JSObject *obj);
   bool AddSQLInfo(JSContext *cx, JSObject *rootObj, bool mainThread);
 
   // Like GetHistogramById, but returns the underlying C++ object, not the JS one.
@@ -92,12 +148,14 @@ private:
   typedef StatisticsRecorder::Histograms::iterator HistogramIterator;
   // This is used for speedy string->Telemetry::ID conversions
   typedef nsBaseHashtableET<nsCharPtrHashKey, Telemetry::ID> CharPtrEntryType;
-  typedef nsTHashtable<CharPtrEntryType> HistogramMapType;
+  typedef AutoHashtable<CharPtrEntryType> HistogramMapType;
   HistogramMapType mHistogramMap;
   bool mCanRecord;
   static TelemetryImpl *sTelemetry;
-  nsTHashtable<SlowSQLEntryType> mSlowSQLOnMainThread;
-  nsTHashtable<SlowSQLEntryType> mSlowSQLOnOtherThread;
+  AutoHashtable<SlowSQLEntryType> mSlowSQLOnMainThread;
+  AutoHashtable<SlowSQLEntryType> mSlowSQLOnOtherThread;
+  // This gets marked immutable in debug builds, so we can't use
+  // AutoHashtable here.
   nsTHashtable<nsCStringHashKey> mTrackedDBs;
   Mutex mHashMutex;
 };
@@ -344,6 +402,7 @@ WrapAndReturnHistogram(Histogram *h, JSContext *cx, jsval *ret)
 }
 
 TelemetryImpl::TelemetryImpl():
+mHistogramMap(Telemetry::HistogramCount),
 mCanRecord(XRE_GetProcessType() == GeckoProcessType_Default),
 mHashMutex("Telemetry::mHashMutex")
 {
@@ -364,16 +423,9 @@ mHashMutex("Telemetry::mHashMutex")
   // Mark immutable to prevent asserts on simultaneous access from multiple threads
   mTrackedDBs.MarkImmutable();
 #endif
-
-  mSlowSQLOnMainThread.Init();
-  mSlowSQLOnOtherThread.Init();
-  mHistogramMap.Init(Telemetry::HistogramCount);
 }
 
 TelemetryImpl::~TelemetryImpl() {
-  mSlowSQLOnMainThread.Clear();
-  mSlowSQLOnOtherThread.Clear();
-  mHistogramMap.Clear();
 }
 
 NS_IMETHODIMP
@@ -387,33 +439,22 @@ TelemetryImpl::NewHistogram(const nsACString &name, PRUint32 min, PRUint32 max,
   return WrapAndReturnHistogram(h, cx, ret);
 }
 
-struct EnumeratorArgs {
-  JSContext *cx;
-  JSObject *statsObj;
-};
-
-PLDHashOperator
-StatementEnumerator(TelemetryImpl::SlowSQLEntryType *entry, void *arg)
+bool
+TelemetryImpl::StatementReflector(SlowSQLEntryType *entry, JSContext *cx,
+                                  JSObject *obj)
 {
-  EnumeratorArgs *args = static_cast<EnumeratorArgs *>(arg);
   const nsACString &sql = entry->GetKey();
   jsval hitCount = UINT_TO_JSVAL(entry->mData.hitCount);
   jsval totalTime = UINT_TO_JSVAL(entry->mData.totalTime);
 
-  JSObject *arrayObj = JS_NewArrayObject(args->cx, 2, nsnull);
-  if (!arrayObj ||
-      !JS_SetElement(args->cx, arrayObj, 0, &hitCount) ||
-      !JS_SetElement(args->cx, arrayObj, 1, &totalTime))
-    return PL_DHASH_STOP;
-
-  JSBool success = JS_DefineProperty(args->cx, args->statsObj,
-                                     sql.BeginReading(),
-                                     OBJECT_TO_JSVAL(arrayObj),
-                                     NULL, NULL, JSPROP_ENUMERATE);
-  if (!success)
-    return PL_DHASH_STOP;
-
-  return PL_DHASH_NEXT;
+  JSObject *arrayObj = JS_NewArrayObject(cx, 2, nsnull);
+  return (arrayObj
+          && JS_SetElement(cx, arrayObj, 0, &hitCount)
+          && JS_SetElement(cx, arrayObj, 1, &totalTime)
+          && JS_DefineProperty(cx, obj,
+                               sql.BeginReading(),
+                               OBJECT_TO_JSVAL(arrayObj),
+                               NULL, NULL, JSPROP_ENUMERATE));
 }
 
 bool
@@ -430,15 +471,10 @@ TelemetryImpl::AddSQLInfo(JSContext *cx, JSObject *rootObj, bool mainThread)
   if (!ok)
     return false;
 
-  EnumeratorArgs args = { cx, statsObj };
-  nsTHashtable<SlowSQLEntryType> *sqlMap;
-  sqlMap = (mainThread ? &mSlowSQLOnMainThread : &mSlowSQLOnOtherThread);
-  PRUint32 num = sqlMap->EnumerateEntries(StatementEnumerator,
-                                          static_cast<void*>(&args));
-  if (num != sqlMap->Count())
-    return false;
-
-  return true;
+  AutoHashtable<SlowSQLEntryType> &sqlMap = (mainThread
+                                             ? mSlowSQLOnMainThread
+                                             : mSlowSQLOnOtherThread);
+  return sqlMap.ReflectHashtable(StatementReflector, cx, statsObj);
 }
 
 nsresult
@@ -731,7 +767,7 @@ TelemetryImpl::RecordSlowStatement(const nsACString &statement,
   if (!sTelemetry->mCanRecord || !sTelemetry->mTrackedDBs.GetEntry(dbName))
     return;
 
-  nsTHashtable<SlowSQLEntryType> *slowSQLMap = NULL;
+  AutoHashtable<SlowSQLEntryType> *slowSQLMap = NULL;
   if (NS_IsMainThread())
     slowSQLMap = &(sTelemetry->mSlowSQLOnMainThread);
   else