--- a/gfx/layers/composite/AsyncCompositionManager.cpp
+++ b/gfx/layers/composite/AsyncCompositionManager.cpp
@@ -675,21 +675,17 @@ SampleAnimations(Layer* aLayer, TimeStam
             (aPoint - animation.startTime()).MultDouble(animation.playbackRate());
           TimingParams timing;
           timing.mDuration.emplace(animation.duration());
           timing.mDelay = animation.delay();
           timing.mIterations = animation.iterations();
           timing.mIterationStart = animation.iterationStart();
           timing.mDirection =
             static_cast<dom::PlaybackDirection>(animation.direction());
-          // Animations typically only run on the compositor during their active
-          // interval but if we end up sampling them outside that range (for
-          // example, while they are waiting to be removed) we currently just
-          // assume that we should fill.
-          timing.mFill = dom::FillMode::Both;
+          timing.mFill = static_cast<dom::FillMode>(animation.fillMode());
           timing.mFunction =
             AnimationUtils::TimingFunctionToComputedTimingFunction(
               animation.easingFunction());
 
           ComputedTiming computedTiming =
             dom::AnimationEffectReadOnly::GetComputedTimingAt(
               Nullable<TimeDuration>(elapsedDuration), timing,
               animation.playbackRate());

--- a/gfx/layers/ipc/LayersMessages.ipdlh
+++ b/gfx/layers/ipc/LayersMessages.ipdlh
@@ -192,16 +192,18 @@ struct Animation {
   AnimationSegment[] segments;
   // Number of times to repeat the animation, including positive infinity.
   // Values <= 0 mean the animation will not play (although events are still
   // dispatched on the main thread).
   float iterations;
   float iterationStart;
   // This uses the NS_STYLE_ANIMATION_DIRECTION_* constants.
   uint8_t direction;
+  // This uses dom::FillMode.
+  uint8_t fillMode;
   nsCSSPropertyID property;
   AnimationData data;
   float playbackRate;
   // This is used in the transformed progress calculation.
   TimingFunction easingFunction;
   uint8_t iterationComposite;
 };
 

--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -426,16 +426,17 @@ AddAnimationForProperty(nsIFrame* aFrame
                               ToTimeStamp(startTime.Value());
   animation->initialCurrentTime() = aAnimation->GetCurrentTime().Value()
                                     - timing.mDelay;
   animation->delay() = timing.mDelay;
   animation->duration() = computedTiming.mDuration;
   animation->iterations() = computedTiming.mIterations;
   animation->iterationStart() = computedTiming.mIterationStart;
   animation->direction() = static_cast<uint8_t>(timing.mDirection);
+  animation->fillMode() = static_cast<uint8_t>(timing.mFill);
   animation->property() = aProperty.mProperty;
   animation->playbackRate() = aAnimation->PlaybackRate();
   animation->data() = aData;
   animation->easingFunction() = ToTimingFunction(timing.mFunction);
   animation->iterationComposite() =
     static_cast<uint8_t>(aAnimation->GetEffect()->
                          AsKeyframeEffect()->IterationComposite());