1 files changed, 17 insertions, 1 deletions
diff --git a/layout/style/nsTransitionManager.h b/layout/style/nsTransitionManager.h
index 56ec61572b..80042adcdf 100644
--- a/layout/style/nsTransitionManager.h
+++ b/layout/style/nsTransitionManager.h
@@ -162,6 +162,18 @@ public:
 
     Animation::CancelFromStyle();
 
+    // The above call to Animation::CancelFromStyle may cause a transitioncancel
+    // event to be queued. However, it will also remove the transition from its
+    // timeline. If this transition was the last animation attached to
+    // the timeline, the timeline will stop observing the refresh driver and
+    // there may be no subsequent tick fro dispatching animation events.
+    //
+    // To ensure the cancel event is dispatched we tell the timeline it needs to
+    // observe the refresh driver for at least one more tick.
+    if (mTimeline) {
+      mTimeline->NotifyAnimationUpdated(*this);
+    }
+
     // It is important we do this *after* calling CancelFromStyle().
     // This is because CancelFromStyle() will end up posting a restyle and
     // that restyle should target the *transitions* level of the cascade.
@@ -214,6 +226,10 @@ public:
       const TimeDuration& aStartTime,
       double aPlaybackRate);
 
+  void MaybeQueueCancelEvent(StickyTimeDuration aActiveTime) override {
+    QueueEvents(aActiveTime);
+  }
+
 protected:
   virtual ~CSSTransition()
   {
@@ -225,7 +241,7 @@ protected:
   void UpdateTiming(SeekFlag aSeekFlag,
                     SyncNotifyFlag aSyncNotifyFlag) override;
 
-  void QueueEvents();
+  void QueueEvents(StickyTimeDuration activeTime = StickyTimeDuration());
 
   // The (pseudo-)element whose computed transition-property refers to this
   // transition (if any).