--- a/accessible/base/NotificationController.cpp
+++ b/accessible/base/NotificationController.cpp
@@ -675,19 +675,18 @@ NotificationController::WillRefresh(mozi
   for (auto iter = mTextHash.Iter(); !iter.Done(); iter.Next()) {
     nsCOMPtrHashKey<nsIContent>* entry = iter.Get();
     nsIContent* textNode = entry->GetKey();
     Accessible* textAcc = mDocument->GetAccessible(textNode);
 
     // If the text node is not in tree or doesn't have a frame, or placed in
     // another document, then this case should have been handled already by
     // content removal notifications.
-    nsINode* containerNode = textNode->GetParentNode();
-    if (!containerNode ||
-        textNode->GetOwnerDocument() != mDocument->DocumentNode()) {
+    nsINode* containerNode = textNode->GetFlattenedTreeParentNode();
+    if (!containerNode || textNode->OwnerDoc() != mDocument->DocumentNode()) {
       MOZ_ASSERT(!textAcc,
                  "Text node was removed but accessible is kept alive!");
       continue;
     }
 
     nsIFrame* textFrame = textNode->GetPrimaryFrame();
     if (!textFrame) {
       MOZ_ASSERT(!textAcc,

--- a/accessible/generic/DocAccessible.cpp
+++ b/accessible/generic/DocAccessible.cpp
@@ -1246,36 +1246,24 @@ DocAccessible::GetAccessibleByUniqueIDIn
 }
 
 Accessible*
 DocAccessible::GetAccessibleOrContainer(nsINode* aNode) const
 {
   if (!aNode || !aNode->GetComposedDoc())
     return nullptr;
 
-  nsINode* currNode = aNode;
-  Accessible* accessible = nullptr;
-  while (!(accessible = GetAccessible(currNode))) {
-    nsINode* parent = nullptr;
-
-    // If this is a content node, try to get a flattened parent content node.
-    // This will smartly skip from the shadow root to the host element,
-    // over parentless document fragment
-    if (currNode->IsContent())
-      parent = currNode->AsContent()->GetFlattenedTreeParent();
-
-    // Fallback to just get parent node, in case there is no parent content
-    // node. Or current node is not a content node.
-    if (!parent)
-      parent = currNode->GetParentNode();
-
-    if (!(currNode = parent)) break;
+  for (nsINode* currNode = aNode; currNode;
+       currNode = currNode->GetFlattenedTreeParentNode()) {
+    if (Accessible* accessible = GetAccessible(currNode)) {
+      return accessible;
+    }
   }
 
-  return accessible;
+  return nullptr;
 }
 
 Accessible*
 DocAccessible::GetAccessibleOrDescendant(nsINode* aNode) const
 {
   Accessible* acc = GetAccessible(aNode);
   if (acc)
     return acc;
@@ -2211,17 +2199,18 @@ DocAccessible::PutChildrenBack(nsTArray<
                       "old parent", owner, "child", child, nullptr);
 #endif
 
     // Unset relocated flag to find an insertion point for the child.
     child->SetRelocated(false);
 
     nsIContent* content = child->GetContent();
     int32_t idxInParent = -1;
-    Accessible* origContainer = AccessibleOrTrueContainer(content->GetParentNode());
+    Accessible* origContainer =
+      AccessibleOrTrueContainer(content->GetFlattenedTreeParentNode());
     if (origContainer) {
       TreeWalker walker(origContainer);
       if (walker.Seek(content)) {
         Accessible* prevChild = walker.Prev();
         if (prevChild) {
           idxInParent = prevChild->IndexInParent() + 1;
           MOZ_DIAGNOSTIC_ASSERT(origContainer == prevChild->Parent(), "Broken tree");
           origContainer = prevChild->Parent();