--- a/layout/base/nsRefreshDriver.cpp
+++ b/layout/base/nsRefreshDriver.cpp
@@ -1889,19 +1889,19 @@ nsRefreshDriver::Tick(int64_t aNowEpoch,
   // Update any popups that may need to be moved or hidden due to their
   // anchor changing.
   nsXULPopupManager* pm = nsXULPopupManager::GetInstance();
   if (pm) {
     pm->UpdatePopupPositions(this);
   }
 #endif
 
-  nsCOMArray<nsIDocument> documents;
+  AutoTArray<nsCOMPtr<nsIDocument>, 32> documents;
   CollectDocuments(mPresContext->Document(), &documents);
-  for (int32_t i = 0; i < documents.Count(); ++i) {
+  for (uint32_t i = 0; i < documents.Length(); ++i) {
     nsIDocument* doc = documents[i];
     doc->UpdateIntersectionObservations();
     doc->ScheduleIntersectionObserverNotification();
   }
 
   /*
    * Perform notification to imgIRequests subscribed to listen
    * for refresh events.