--- a/dom/animation/KeyframeEffect.cpp
+++ b/dom/animation/KeyframeEffect.cpp
@@ -246,17 +246,17 @@ KeyframeEffectReadOnly::GetComputedTimin
              "mIterations should be nonnegative & finite, as ensured by "
              "ValidateIterations or CSSParser");
   result.mIterations = aTiming.mIterations;
   MOZ_ASSERT(aTiming.mIterationStart >= 0.0,
              "mIterationStart should be nonnegative, as ensured by "
              "ValidateIterationStart");
   result.mIterationStart = aTiming.mIterationStart;
 
-  result.mActiveDuration = ActiveDuration(result.mDuration, result.mIterations);
+  result.mActiveDuration = aTiming.ActiveDuration();
   result.mEndTime = aTiming.mDelay + result.mActiveDuration +
                     aTiming.mEndDelay;
   result.mFill = aTiming.mFill == dom::FillMode::Auto ?
                  dom::FillMode::None :
                  aTiming.mFill;
 
   // The default constructor for ComputedTiming sets all other members to
   // values consistent with an animation that has not been sampled.
@@ -399,33 +399,16 @@ KeyframeEffectReadOnly::GetComputedTimin
     result.mProgress.SetValue(
       aTiming.mFunction->GetValue(result.mProgress.Value(),
                                   result.mBeforeFlag));
   }
 
   return result;
 }
 
-StickyTimeDuration
-KeyframeEffectReadOnly::ActiveDuration(
-  const StickyTimeDuration& aIterationDuration,
-  double aIterationCount)
-{
-  // If either the iteration duration or iteration count is zero,
-  // Web Animations says that the active duration is zero. This is to
-  // ensure that the result is defined when the other argument is Infinity.
-  const StickyTimeDuration zeroDuration;
-  if (aIterationDuration == zeroDuration ||
-      aIterationCount == 0.0) {
-    return zeroDuration;
-  }
-
-  return aIterationDuration.MultDouble(aIterationCount);
-}
-
 // https://w3c.github.io/web-animations/#in-play
 bool
 KeyframeEffectReadOnly::IsInPlay() const
 {
   if (!mAnimation || mAnimation->PlayState() == AnimationPlayState::Finished) {
     return false;
   }
 

--- a/dom/animation/KeyframeEffect.h
+++ b/dom/animation/KeyframeEffect.h
@@ -269,22 +269,16 @@ public:
   {
     return GetComputedTimingAt(GetLocalTime(),
                                aTiming ? *aTiming : SpecifiedTiming());
   }
 
   void
   GetComputedTimingAsDict(ComputedTimingProperties& aRetVal) const override;
 
-  // Return the duration of the active interval for the given duration and
-  // iteration count.
-  static StickyTimeDuration
-  ActiveDuration(const StickyTimeDuration& aIterationDuration,
-                 double aIterationCount);
-
   bool IsInPlay() const;
   bool IsCurrent() const;
   bool IsInEffect() const;
 
   void SetAnimation(Animation* aAnimation);
   Animation* GetAnimation() const { return mAnimation; }
 
   void SetFrames(nsTArray<Keyframe>&& aFrames, nsStyleContext* aStyleContext);

--- a/dom/animation/TimingParams.h
+++ b/dom/animation/TimingParams.h
@@ -92,16 +92,31 @@ struct TimingParams
   TimeDuration mDelay;      // Initializes to zero
   TimeDuration mEndDelay;
   double mIterations = 1.0; // Can be NaN, negative, +/-Infinity
   double mIterationStart = 0.0;
   dom::PlaybackDirection mDirection = dom::PlaybackDirection::Normal;
   dom::FillMode mFill = dom::FillMode::Auto;
   Maybe<ComputedTimingFunction> mFunction;
 
+  // Return the duration of the active interval calculated by duration and
+  // iteration count.
+  StickyTimeDuration ActiveDuration() const
+  {
+    // If either the iteration duration or iteration count is zero,
+    // Web Animations says that the active duration is zero. This is to
+    // ensure that the result is defined when the other argument is Infinity.
+    static const StickyTimeDuration zeroDuration;
+    if (!mDuration || *mDuration == zeroDuration || mIterations == 0.0) {
+      return zeroDuration;
+    }
+
+    return mDuration->MultDouble(mIterations);
+  }
+
   bool operator==(const TimingParams& aOther) const;
   bool operator!=(const TimingParams& aOther) const
   {
     return !(*this == aOther);
   }
 };
 
 } // namespace mozilla