--- a/dom/media/Intervals.h
+++ b/dom/media/Intervals.h
@@ -6,16 +6,30 @@
 
 #ifndef INTERVALS_H
 #define INTERVALS_H
 
 #include <algorithm>
 #include "mozilla/TypeTraits.h"
 #include "nsTArray.h"
 
+// Specialization for nsTArray CopyChooser.
+namespace mozilla {
+namespace media {
+template<class T>
+class IntervalSet;
+}
+}
+
+template<class E>
+struct nsTArray_CopyChooser<mozilla::media::IntervalSet<E>>
+{
+  typedef nsTArray_CopyWithConstructors<mozilla::media::IntervalSet<E>> Type;
+};
+
 namespace mozilla {
 namespace media {
 
 /* Interval defines an interval between two points. Unlike a traditional
    interval [A,B] where A <= x <= B, the upper boundary B is exclusive: A <= x < B
    (e.g [A,B[ or [A,B) depending on where you're living)
    It provides basic interval arithmetic and fuzzy edges.
    The type T must provides a default constructor and +, -, <, <= and ==

--- a/dom/media/TimeUnits.h
+++ b/dom/media/TimeUnits.h
@@ -9,16 +9,28 @@
 
 #include "Intervals.h"
 #include "mozilla/CheckedInt.h"
 #include "mozilla/FloatingPoint.h"
 #include "mozilla/dom/TimeRanges.h"
 
 namespace mozilla {
 namespace media {
+class TimeIntervals;
+}
+}
+// CopyChooser specalization for nsTArray
+template<>
+struct nsTArray_CopyChooser<mozilla::media::TimeIntervals>
+{
+  typedef nsTArray_CopyWithConstructors<mozilla::media::TimeIntervals> Type;
+};
+
+namespace mozilla {
+namespace media {
 
 // Number of microseconds per second. 1e6.
 static const int64_t USECS_PER_S = 1000000;
 
 // Number of microseconds per millisecond.
 static const int64_t USECS_PER_MS = 1000;
 
 // Number of nanoseconds per second. 1e9.

--- a/dom/media/gtest/TestIntervalSet.cpp
+++ b/dom/media/gtest/TestIntervalSet.cpp
@@ -704,8 +704,17 @@ TEST(IntervalSet, FooIntervalSet)
   is += i;
   is.Add(i);
   is = is + i;
   is = i + is;
   EXPECT_EQ(1u, is.Length());
   EXPECT_EQ(Foo<int>(), is[0].mStart);
   EXPECT_EQ(Foo<int>(4,5,6), is[0].mEnd);
 }
+
+TEST(IntervalSet, StaticAssert)
+{
+  typedef media::IntervalSet<int> IntIntervals;
+  media::Interval<int> i;
+
+  static_assert(mozilla::IsSame<nsTArray_CopyChooser<IntIntervals>::Type, nsTArray_CopyWithConstructors<IntIntervals>>::value, "Must use copy constructor");
+  static_assert(mozilla::IsSame<nsTArray_CopyChooser<media::TimeIntervals>::Type, nsTArray_CopyWithConstructors<media::TimeIntervals>>::value, "Must use copy constructor");
+}