--- a/layout/base/AccessibleCaretEventHub.cpp
+++ b/layout/base/AccessibleCaretEventHub.cpp
@@ -395,18 +395,25 @@ AccessibleCaretEventHub::Init()
   nsPresContext* presContext = mPresShell->GetPresContext();
   MOZ_ASSERT(presContext, "PresContext should be given in PresShell::Init()");
 
   nsIDocShell* docShell = presContext->GetDocShell();
   if (!docShell) {
     return;
   }
 
-  docShell->AddWeakReflowObserver(this);
-  docShell->AddWeakScrollObserver(this);
+  nsCOMPtr<nsIDocShell> curDocShell = docShell;
+  do {
+    curDocShell->AddWeakReflowObserver(this);
+    curDocShell->AddWeakScrollObserver(this);
+
+    nsCOMPtr<nsIDocShellTreeItem> tmp;
+    curDocShell->GetSameTypeParent(getter_AddRefs(tmp));
+    curDocShell = do_QueryInterface(tmp);
+  } while (curDocShell);
 
   mDocShell = static_cast<nsDocShell*>(docShell);
 
   if (sUseLongTapInjector) {
     mLongTapInjectorTimer = NS_NewTimer();
   }
 
   mManager = MakeUnique<AccessibleCaretManager>(mPresShell);
@@ -416,20 +423,24 @@ AccessibleCaretEventHub::Init()
 
 void
 AccessibleCaretEventHub::Terminate()
 {
   if (!mInitialized) {
     return;
   }
 
-  RefPtr<nsDocShell> docShell(mDocShell.get());
-  if (docShell) {
-    docShell->RemoveWeakReflowObserver(this);
-    docShell->RemoveWeakScrollObserver(this);
+  nsCOMPtr<nsIDocShell> curDocShell = mDocShell.get();
+  while (curDocShell) {
+    curDocShell->RemoveWeakReflowObserver(this);
+    curDocShell->RemoveWeakScrollObserver(this);
+
+    nsCOMPtr<nsIDocShellTreeItem> tmp;
+    curDocShell->GetSameTypeParent(getter_AddRefs(tmp));
+    curDocShell = do_QueryInterface(tmp);
   }
 
   if (mLongTapInjectorTimer) {
     mLongTapInjectorTimer->Cancel();
   }
 
   mManager->Terminate();
   mPresShell = nullptr;