--- a/dom/animation/AnimationPlayer.cpp
+++ b/dom/animation/AnimationPlayer.cpp
@@ -344,17 +344,19 @@ AnimationPlayer::Cancel()
   mStartTime.SetNull();
 
   UpdateSourceContent();
 }
 
 bool
 AnimationPlayer::IsRunning() const
 {
-  if (IsPaused() || !GetSource() || GetSource()->IsFinishedTransition()) {
+  if (IsPausedOrPausing() ||
+      !GetSource() ||
+      GetSource()->IsFinishedTransition()) {
     return false;
   }
 
   ComputedTiming computedTiming = GetSource()->GetComputedTiming();
   return computedTiming.mPhase == ComputedTiming::AnimationPhase_Active;
 }
 
 void

--- a/dom/animation/AnimationPlayer.h
+++ b/dom/animation/AnimationPlayer.h
@@ -186,27 +186,34 @@ public:
    * This method returns the start time, if resolved. Otherwise, if we have
    * a pending ready time, it returns the corresponding start time. If neither
    * of those are available, it returns null.
    */
   Nullable<TimeDuration> GetCurrentOrPendingStartTime() const;
 
   void Cancel();
 
-  const nsString& Name() const {
+  const nsString& Name() const
+  {
     return mSource ? mSource->Name() : EmptyString();
   }
 
-  bool IsPaused() const { return PlayState() == AnimationPlayState::Paused; }
+  bool IsPausedOrPausing() const
+  {
+    return PlayState() == AnimationPlayState::Paused ||
+           mPendingState == PendingState::PausePending;
+  }
   bool IsRunning() const;
 
-  bool HasCurrentSource() const {
+  bool HasCurrentSource() const
+  {
     return GetSource() && GetSource()->IsCurrent();
   }
-  bool HasInEffectSource() const {
+  bool HasInEffectSource() const
+  {
     return GetSource() && GetSource()->IsInEffect();
   }
 
   bool IsRelevant() const { return mIsRelevant; }
   void UpdateRelevance();
 
   void SetIsRunningOnCompositor() { mIsRunningOnCompositor = true; }
   void ClearIsRunningOnCompositor() { mIsRunningOnCompositor = false; }

--- a/layout/style/nsAnimationManager.cpp
+++ b/layout/style/nsAnimationManager.cpp
@@ -343,21 +343,22 @@ nsAnimationManager::CheckAnimationRule(n
 
         // Handle changes in play state.
         // CSSAnimationPlayer takes care of override behavior so that,
         // for example, if the author has called pause(), that will
         // override the animation-play-state.
         // (We should check newPlayer->IsStylePaused() but that requires
         //  downcasting to CSSAnimationPlayer and we happen to know that
         //  newPlayer will only ever be paused by calling PauseFromStyle
-        //  making IsPaused synonymous in this case.)
-        if (!oldPlayer->IsStylePaused() && newPlayer->IsPaused()) {
+        //  making IsPausedOrPausing synonymous in this case.)
+        if (!oldPlayer->IsStylePaused() && newPlayer->IsPausedOrPausing()) {
           oldPlayer->PauseFromStyle();
           animationChanged = true;
-        } else if (oldPlayer->IsStylePaused() && !newPlayer->IsPaused()) {
+        } else if (oldPlayer->IsStylePaused() &&
+                   !newPlayer->IsPausedOrPausing()) {
           oldPlayer->PlayFromStyle();
           animationChanged = true;
         }
 
         if (animationChanged) {
           nsNodeUtils::AnimationChanged(oldPlayer);
         }