--- a/dom/base/ElementInlines.h
+++ b/dom/base/ElementInlines.h
@@ -62,16 +62,17 @@ Element::NoteDirtyDescendantsForServo()
   Element* curr = this;
   while (curr && !curr->HasDirtyDescendantsForServo()) {
     curr->SetHasDirtyDescendantsForServo();
     curr = curr->GetFlattenedTreeParentElementForStyle();
   }
 
   if (nsIPresShell* shell = OwnerDoc()->GetShell()) {
     shell->SetNeedStyleFlush();
+    shell->ObserveStyleFlushes();
   }
 
   MOZ_ASSERT(DirtyDescendantsBitIsPropagatedForServo());
 }
 
 #ifdef DEBUG
 inline bool
 Element::DirtyDescendantsBitIsPropagatedForServo()