diff --git a/accessible/generic/DocAccessible.cpp b/accessible/generic/DocAccessible.cpp
index 3a4a657fcab6..4367a1ec4d4f 100644
--- a/accessible/generic/DocAccessible.cpp
+++ b/accessible/generic/DocAccessible.cpp
@@ -1130,10 +1130,28 @@ Accessible* DocAccessible::GetAccessibleByUniqueIDInSubtree(void* aUniqueID) {
 
 Accessible* DocAccessible::GetAccessibleOrContainer(nsINode* aNode,
                                                     int aARIAHiddenFlag) const {
-  if (!aNode || !aNode->GetComposedDoc()) return nullptr;
+  if (!aNode || !aNode->GetComposedDoc()) {
+    return nullptr;
+  }
 
-  for (nsINode* currNode = aNode; currNode;
-       currNode = currNode->GetFlattenedTreeParentNode()) {
+  nsINode* currNode = nullptr;
+  if (aNode->IsShadowRoot()) {
+    // This can happen, for example, when called within
+    // SelectionManager::ProcessSelectionChanged due to focusing a direct
+    // child of a shadow root.
+    // GetFlattenedTreeParent works on children of a shadow root, but not the
+    // shadow root itself.
+    const dom::ShadowRoot* shadowRoot = dom::ShadowRoot::FromNode(aNode);
+    currNode = shadowRoot->GetHost();
+    if (!currNode) {
+      return nullptr;
+    }
+  } else {
+    currNode = aNode;
+  }
+
+  MOZ_ASSERT(currNode);
+  for (; currNode; currNode = currNode->GetFlattenedTreeParentNode()) {
     // No container if is inside of aria-hidden subtree.
     if (aARIAHiddenFlag == eNoContainerIfARIAHidden && currNode->IsElement() &&
         aria::HasDefinedARIAHidden(currNode->AsElement())) {