--- a/dom/animation/Animation.cpp
+++ b/dom/animation/Animation.cpp
@@ -665,22 +665,17 @@ Animation::SilentlySetPlaybackRate(doubl
     SilentlySetCurrentTime(previousTime.Value());
   }
 }
 
 // https://w3c.github.io/web-animations/#cancel-an-animation
 void
 Animation::CancelNoUpdate()
 {
-  if (mPendingState != PendingState::NotPending) {
-    CancelPendingTasks();
-    if (mReady) {
-      mReady->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
-    }
-  }
+  ResetPendingTasks();
 
   if (mFinished) {
     mFinished->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
   }
   ResetFinishedPromise();
 
   DispatchPlaybackEvent(NS_LITERAL_STRING("cancel"));
 
@@ -1167,16 +1162,30 @@ Animation::CancelPendingTasks()
       }
     }
   }
 
   mPendingState = PendingState::NotPending;
   mPendingReadyTime.SetNull();
 }
 
+// https://w3c.github.io/web-animations/#reset-an-animations-pending-tasks
+void
+Animation::ResetPendingTasks()
+{
+  if (mPendingState == PendingState::NotPending) {
+    return;
+  }
+
+  CancelPendingTasks();
+  if (mReady) {
+    mReady->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+  }
+}
+
 bool
 Animation::IsPossiblyOrphanedPendingAnimation() const
 {
   // Check if we are pending but might never start because we are not being
   // tracked.
   //
   // This covers the following cases:
   //

--- a/dom/animation/Animation.h
+++ b/dom/animation/Animation.h
@@ -365,16 +365,22 @@ protected:
 
   /**
    * Remove this animation from the pending animation tracker and reset
    * mPendingState as necessary. The caller is responsible for resolving or
    * aborting the mReady promise as necessary.
    */
   void CancelPendingTasks();
 
+  /**
+   * Performs the same steps as CancelPendingTasks and also rejects and
+   * recreates the ready promise if the animation was pending.
+   */
+  void ResetPendingTasks();
+
   bool IsPossiblyOrphanedPendingAnimation() const;
   StickyTimeDuration EffectEnd() const;
 
   nsIDocument* GetRenderedDocument() const;
 
   RefPtr<AnimationTimeline> mTimeline;
   RefPtr<AnimationEffectReadOnly> mEffect;
   // The beginning of the delay period.