--- a/toolkit/components/telemetry/Telemetry.cpp
+++ b/toolkit/components/telemetry/Telemetry.cpp
@@ -8,16 +8,17 @@
 
 #include <fstream>
 
 #include <prio.h>
 
 #include "mozilla/Attributes.h"
 #include "mozilla/DebugOnly.h"
 #include "mozilla/Likely.h"
+#include "mozilla/MathAlgorithms.h"
 
 #include "base/histogram.h"
 #include "base/pickle.h"
 #include "nsIComponentManager.h"
 #include "nsIServiceManager.h"
 #include "nsThreadManager.h"
 #include "nsCOMArray.h"
 #include "nsCOMPtr.h"
@@ -2434,16 +2435,51 @@ WriteFailedProfileLock(nsIFile* aProfile
       break;
     }
     bytes += written;
     bytesLeft -= written;
   } while (bytesLeft > 0);
   seekStream->SetEOF();
 }
 
+
+void
+TimeHistogram::Add(PRIntervalTime aTime)
+{
+  uint32_t timeMs = PR_IntervalToMilliseconds(aTime);
+  size_t index = mozilla::FloorLog2(timeMs);
+  operator[](index)++;
+}
+
+uint32_t
+HangHistogram::GetHash(const Stack& aStack)
+{
+  uint32_t hash = 0;
+  for (const char* const* label = aStack.begin();
+       label != aStack.end(); label++) {
+    /* We only need to hash the pointer instead of the text content
+       because we are assuming constant pointers */
+    hash = AddToHash(hash, *label);
+  }
+  return hash;
+}
+
+bool
+HangHistogram::operator==(const HangHistogram& aOther) const
+{
+  if (mHash != aOther.mHash) {
+    return false;
+  }
+  if (mStack.length() != aOther.mStack.length()) {
+    return false;
+  }
+  return PodEqual(mStack.begin(), aOther.mStack.begin(), mStack.length());
+}
+
+
 } // namespace Telemetry
 } // namespace mozilla
 
 NSMODULE_DEFN(nsTelemetryModule) = &kTelemetryModule;
 
 /**
  * The XRE_TelemetryAdd function is to be used by embedding applications
  * that can't use mozilla::Telemetry::Accumulate() directly.

new file mode 100644
--- /dev/null
+++ b/toolkit/components/telemetry/ThreadHangStats.h
@@ -0,0 +1,102 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_BackgroundHangTelemetry_h
+#define mozilla_BackgroundHangTelemetry_h
+
+#include "mozilla/Array.h"
+#include "mozilla/Move.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/Vector.h"
+
+#include "nsString.h"
+#include "prinrval.h"
+
+namespace mozilla {
+namespace Telemetry {
+
+static const size_t kTimeHistogramBuckets = 8 * sizeof(PRIntervalTime);
+
+/* TimeHistogram is an efficient histogram that puts time durations into
+   exponential (base 2) buckets; times are accepted in PRIntervalTime and
+   stored in milliseconds. */
+class TimeHistogram : public mozilla::Array<uint32_t, kTimeHistogramBuckets>
+{
+public:
+  TimeHistogram()
+  {
+    mozilla::PodArrayZero(*this);
+  }
+  void Add(PRIntervalTime aTime);
+};
+
+/* A hang histogram consists of a stack associated with the
+   hang, along with a time histogram of the hang times. */
+class HangHistogram : public TimeHistogram
+{
+public:
+  typedef mozilla::Vector<const char*, 8> Stack;
+
+private:
+  static uint32_t GetHash(const Stack& aStack);
+
+  Stack mStack;
+  // Use a hash to speed comparisons
+  const uint32_t mHash;
+
+public:
+  explicit HangHistogram(Stack&& aStack)
+    : mStack(mozilla::Move(aStack))
+    , mHash(GetHash(mStack))
+  {
+  }
+  HangHistogram(HangHistogram&& aOther)
+    : TimeHistogram(mozilla::Move(aOther))
+    , mStack(mozilla::Move(aOther.mStack))
+    , mHash(mozilla::Move(aOther.mHash))
+  {
+  }
+  bool operator==(const HangHistogram& aOther) const;
+  bool operator!=(const HangHistogram& aOther) const
+  {
+    return !operator==(aOther);
+  }
+  const Stack& GetStack() const {
+    return mStack;
+  }
+};
+
+/* Thread hang stats consist of
+ - thread name
+ - time histogram of all task run times
+ - hang histograms of individual hangs. */
+class ThreadHangStats
+{
+private:
+  nsAutoCString mName;
+
+public:
+  TimeHistogram mActivity;
+  mozilla::Vector<HangHistogram, 4> mHangs;
+
+  explicit ThreadHangStats(const char* aName)
+    : mName(aName)
+  {
+  }
+  ThreadHangStats(ThreadHangStats&& aOther)
+    : mName(mozilla::Move(aOther.mName))
+    , mActivity(mozilla::Move(aOther.mActivity))
+    , mHangs(mozilla::Move(aOther.mHangs))
+  {
+  }
+  const char* GetName() const {
+    return mName.get();
+  }
+};
+
+} // namespace Telemetry
+} // namespace mozilla
+#endif // mozilla_BackgroundHangTelemetry_h

--- a/toolkit/components/telemetry/moz.build
+++ b/toolkit/components/telemetry/moz.build
@@ -11,16 +11,17 @@ XPIDL_SOURCES += [
     'nsITelemetryPing.idl',
 ]
 
 XPIDL_MODULE = 'telemetry'
 
 EXPORTS.mozilla += [
     'ProcessedStack.h',
     'Telemetry.h',
+    'ThreadHangStats.h',
 ]
 
 SOURCES += [
     'Telemetry.cpp',
 ]
 
 EXTRA_COMPONENTS += [
     'TelemetryPing.manifest',