diff --git a/mfbt/ReverseIterator.h b/mfbt/ReverseIterator.h
new file mode 100644
index 00000000000..e9b2d9b8a04
--- /dev/null
+++ b/mfbt/ReverseIterator.h
@@ -0,0 +1,190 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+/* An iterator that acts like another iterator, but iterating in
+ * the negative direction. (Note that not all iterators can iterate
+ * in the negative direction.) */
+
+#ifndef mozilla_ReverseIterator_h
+#define mozilla_ReverseIterator_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/IteratorTraits.h"
+
+namespace mozilla {
+
+template<typename IteratorT>
+class ReverseIterator
+{
+public:
+  typedef typename IteratorTraits<IteratorT>::ValueType ValueType;
+  typedef typename IteratorTraits<IteratorT>::DifferenceType DifferenceType;
+
+  template<typename Iterator>
+  explicit ReverseIterator(Iterator aIter)
+    : mCurrent(aIter) { }
+
+  template<typename Iterator>
+  MOZ_IMPLICIT ReverseIterator(const ReverseIterator<Iterator>& aOther)
+    : mCurrent(aOther.mCurrent) { }
+
+  ValueType& operator*() const
+  {
+    IteratorT tmp = mCurrent;
+    return *--tmp;
+  }
+
+  /* Increments and decrements operators */
+
+  ReverseIterator& operator++() { --mCurrent; return *this; }
+  ReverseIterator& operator--() { ++mCurrent; return *this; }
+  ReverseIterator operator++(int) { auto ret = *this; mCurrent--; return ret; }
+  ReverseIterator operator--(int) { auto ret = *this; mCurrent++; return ret; }
+
+  ReverseIterator operator+(DifferenceType aN) const
+  {
+    return ReverseIterator(mCurrent - aN);
+  }
+  ReverseIterator operator-(DifferenceType aN) const
+  {
+    return ReverseIterator(mCurrent + aN);
+  }
+  ReverseIterator& operator+=(DifferenceType aN)
+  {
+    mCurrent -= aN;
+    return *this;
+  }
+  ReverseIterator& operator-=(DifferenceType aN)
+  {
+    mCurrent += aN;
+    return *this;
+  }
+
+  /* Comparison operators */
+
+  template<typename Iterator1, typename Iterator2>
+  friend bool operator==(const ReverseIterator<Iterator1>& aIter1,
+                         const ReverseIterator<Iterator2>& aIter2);
+  template<typename Iterator1, typename Iterator2>
+  friend bool operator!=(const ReverseIterator<Iterator1>& aIter1,
+                         const ReverseIterator<Iterator2>& aIter2);
+  template<typename Iterator1, typename Iterator2>
+  friend bool operator<(const ReverseIterator<Iterator1>& aIter1,
+                        const ReverseIterator<Iterator2>& aIter2);
+  template<typename Iterator1, typename Iterator2>
+  friend bool operator<=(const ReverseIterator<Iterator1>& aIter1,
+                         const ReverseIterator<Iterator2>& aIter2);
+  template<typename Iterator1, typename Iterator2>
+  friend bool operator>(const ReverseIterator<Iterator1>& aIter1,
+                        const ReverseIterator<Iterator2>& aIter2);
+  template<typename Iterator1, typename Iterator2>
+  friend bool operator>=(const ReverseIterator<Iterator1>& aIter1,
+                         const ReverseIterator<Iterator2>& aIter2);
+
+private:
+  IteratorT mCurrent;
+};
+
+template<typename Iterator1, typename Iterator2>
+bool
+operator==(const ReverseIterator<Iterator1>& aIter1,
+           const ReverseIterator<Iterator2>& aIter2)
+{
+  return aIter1.mCurrent == aIter2.mCurrent;
+}
+
+template<typename Iterator1, typename Iterator2>
+bool
+operator!=(const ReverseIterator<Iterator1>& aIter1,
+           const ReverseIterator<Iterator2>& aIter2)
+{
+  return aIter1.mCurrent != aIter2.mCurrent;
+}
+
+template<typename Iterator1, typename Iterator2>
+bool
+operator<(const ReverseIterator<Iterator1>& aIter1,
+          const ReverseIterator<Iterator2>& aIter2)
+{
+  return aIter1.mCurrent > aIter2.mCurrent;
+}
+
+template<typename Iterator1, typename Iterator2>
+bool
+operator<=(const ReverseIterator<Iterator1>& aIter1,
+           const ReverseIterator<Iterator2>& aIter2)
+{
+  return aIter1.mCurrent >= aIter2.mCurrent;
+}
+
+template<typename Iterator1, typename Iterator2>
+bool
+operator>(const ReverseIterator<Iterator1>& aIter1,
+          const ReverseIterator<Iterator2>& aIter2)
+{
+  return aIter1.mCurrent < aIter2.mCurrent;
+}
+
+template<typename Iterator1, typename Iterator2>
+bool
+operator>=(const ReverseIterator<Iterator1>& aIter1,
+           const ReverseIterator<Iterator2>& aIter2)
+{
+  return aIter1.mCurrent <= aIter2.mCurrent;
+}
+
+namespace detail {
+
+template<typename IteratorT>
+class IteratorRange
+{
+public:
+  typedef IteratorT iterator;
+  typedef IteratorT const_iterator;
+  typedef ReverseIterator<IteratorT> reverse_iterator;
+  typedef ReverseIterator<IteratorT> const_reverse_iterator;
+
+  template<typename Iterator1, typename Iterator2>
+  IteratorRange(Iterator1 aIterBegin, Iterator2 aIterEnd)
+    : mIterBegin(aIterBegin), mIterEnd(aIterEnd) { }
+
+  template<typename Iterator>
+  IteratorRange(const IteratorRange<Iterator>& aOther)
+    : mIterBegin(aOther.mIterBegin), mIterEnd(aOther.mIterEnd) { }
+
+  iterator begin() const { return mIterBegin; }
+  const_iterator cbegin() const { return begin(); }
+  iterator end() const { return mIterEnd; }
+  const_iterator cend() const { return end(); }
+  reverse_iterator rbegin() const { return reverse_iterator(mIterEnd); }
+  const_reverse_iterator crbegin() const { return rbegin(); }
+  reverse_iterator rend() const { return reverse_iterator(mIterBegin); }
+  const_reverse_iterator crend() const { return rend(); }
+
+private:
+  IteratorT mIterBegin;
+  IteratorT mIterEnd;
+};
+
+} // namespace detail
+
+template<typename Range>
+detail::IteratorRange<typename Range::reverse_iterator>
+Reversed(Range& aRange)
+{
+  return {aRange.rbegin(), aRange.rend()};
+}
+
+template<typename Range>
+detail::IteratorRange<typename Range::const_reverse_iterator>
+Reversed(const Range& aRange)
+{
+  return {aRange.rbegin(), aRange.rend()};
+}
+
+} // namespace mozilla
+
+#endif // mozilla_ReverseIterator_h
diff --git a/mfbt/moz.build b/mfbt/moz.build
index b1bf1e73e4b..921bc8d0c1d 100644
--- a/mfbt/moz.build
+++ b/mfbt/moz.build
@@ -60,6 +60,7 @@ EXPORTS.mozilla = [
     'RefCountType.h',
     'ReentrancyGuard.h',
     'RefPtr.h',
+    'ReverseIterator.h',
     'RollingMean.h',
     'Scoped.h',
     'SegmentedVector.h',