--- a/dom/animation/KeyframeEffect.h
+++ b/dom/animation/KeyframeEffect.h
@@ -83,20 +83,23 @@ struct PropertyValuePair
  *
  * When the target element or style context changes, however, we rebuild these
  * per-property arrays from the original list of keyframes objects. As a result,
  * these objects represent the master definition of the effect's values.
  */
 struct Keyframe
 {
   Keyframe() = default;
+  Keyframe(const Keyframe& aOther) = default;
   Keyframe(Keyframe&& aOther)
   {
     *this = Move(aOther);
   }
+
+  Keyframe& operator=(const Keyframe& aOther) = default;
   Keyframe& operator=(Keyframe&& aOther)
   {
     mOffset         = aOther.mOffset;
     mComputedOffset = aOther.mComputedOffset;
     mTimingFunction = Move(aOther.mTimingFunction);
     mPropertyValues = Move(aOther.mPropertyValues);
     return *this;
   }