diff --git a/dom/animation/Animation.cpp b/dom/animation/Animation.cpp
--- a/dom/animation/Animation.cpp
+++ b/dom/animation/Animation.cpp
@@ -1716,10 +1716,11 @@
   RefPtr<Animation> mAnimation;
 };
 
 void Animation::DoFinishNotification(SyncNotifyFlag aSyncNotifyFlag) {
   CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
+  variable++;
 
   if (aSyncNotifyFlag == SyncNotifyFlag::Sync) {
     DoFinishNotificationImmediately();
   } else if (!mFinishNotificationTask) {
     RefPtr<MicroTaskRunnable> runnable = new AsyncFinishNotification(this);