--- a/editor/libeditor/EditorBase.cpp
+++ b/editor/libeditor/EditorBase.cpp
@@ -2737,22 +2737,24 @@ EditorBase::CreateTxnForSplitNode(nsICon
     new SplitNodeTransaction(*this, aNode, aOffset);
   return transaction.forget();
 }
 
 already_AddRefed<JoinNodeTransaction>
 EditorBase::CreateTxnForJoinNode(nsINode& aLeftNode,
                                  nsINode& aRightNode)
 {
-  RefPtr<JoinNodeTransaction> transaction =
+  RefPtr<JoinNodeTransaction> joinNodeTransaction =
     new JoinNodeTransaction(*this, aLeftNode, aRightNode);
-
-  NS_ENSURE_SUCCESS(transaction->CheckValidity(), nullptr);
-
-  return transaction.forget();
+  // If it's not editable, the transaction shouldn't be recorded since it
+  // should never be undone/redone.
+  if (NS_WARN_IF(!joinNodeTransaction->CanDoIt())) {
+    return nullptr;
+  }
+  return joinNodeTransaction.forget();
 }
 
 struct SavedRange final
 {
   RefPtr<Selection> mSelection;
   nsCOMPtr<nsINode> mStartNode;
   nsCOMPtr<nsINode> mEndNode;
   int32_t mStartOffset;

--- a/editor/libeditor/JoinNodeTransaction.cpp
+++ b/editor/libeditor/JoinNodeTransaction.cpp
@@ -31,23 +31,25 @@ JoinNodeTransaction::JoinNodeTransaction
 NS_IMPL_CYCLE_COLLECTION_INHERITED(JoinNodeTransaction, EditTransactionBase,
                                    mLeftNode,
                                    mRightNode,
                                    mParent)
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(JoinNodeTransaction)
 NS_INTERFACE_MAP_END_INHERITING(EditTransactionBase)
 
-nsresult
-JoinNodeTransaction::CheckValidity()
+bool
+JoinNodeTransaction::CanDoIt() const
 {
-  if (!mEditorBase.IsModifiableNode(mLeftNode->GetParentNode())) {
-    return NS_ERROR_FAILURE;
+  if (NS_WARN_IF(!mLeftNode) ||
+      NS_WARN_IF(!mRightNode) ||
+      !mLeftNode->GetParentNode()) {
+    return false;
   }
-  return NS_OK;
+  return mEditorBase.IsModifiableNode(mLeftNode->GetParentNode());
 }
 
 // After DoTransaction() and RedoTransaction(), the left node is removed from
 // the content tree and right node remains.
 NS_IMETHODIMP
 JoinNodeTransaction::DoTransaction()
 {
   // Get the parent node

--- a/editor/libeditor/JoinNodeTransaction.h
+++ b/editor/libeditor/JoinNodeTransaction.h
@@ -31,19 +31,20 @@ public:
    * @param aEditorBase     The provider of core editing operations.
    * @param aLeftNode       The first of two nodes to join.
    * @param aRightNode      The second of two nodes to join.
    */
   JoinNodeTransaction(EditorBase& aEditorBase,
                       nsINode& aLeftNode, nsINode& aRightNode);
 
   /**
-   * Call this after constructing to ensure the inputs are correct.
+   * CanDoIt() returns true if there are enough members and can join or
+   * restore the nodes.  Otherwise, false.
    */
-  nsresult CheckValidity();
+  bool CanDoIt() const;
 
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(JoinNodeTransaction,
                                            EditTransactionBase)
   NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override;
 
   NS_DECL_EDITTRANSACTIONBASE
 
 protected: