diff --git a/dom/animation/Animation.cpp b/dom/animation/Animation.cpp
--- a/dom/animation/Animation.cpp
+++ b/dom/animation/Animation.cpp
@@ -1718,6 +1718,7 @@
 
 void Animation::DoFinishNotification(SyncNotifyFlag aSyncNotifyFlag) {
   CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
+  variable++;
 
   if (aSyncNotifyFlag == SyncNotifyFlag::Sync) {
     DoFinishNotificationImmediately();