Bug 1656419 - Check whether the given animation and the animation stored in mPartialPrerenderedAnimations are in the same EffectSet instead of just comparing the animation instances. r=boris

Differential Revision: https://phabricator.services.mozilla.com/D85535

dom/animation/KeyframeEffect.cpp

@@ -904,8 +904,12 @@ void KeyframeEffect::UpdateTarget(Element* aElement,
   }
 
   if (mTarget) {
-    UnregisterTarget();
+    // Call ResetIsRunningOnCompositor() prior to UnregisterTarget() since
+    // ResetIsRunningOnCompositor() might try to get the EffectSet associated
+    // with this keyframe effect to remove partial pre-render animation from
+    // the layer manager.
     ResetIsRunningOnCompositor();
+    UnregisterTarget();
 
     RequestRestyle(EffectCompositor::RestyleType::Layer);