--- a/editor/libeditor/HTMLEditRules.cpp
+++ b/editor/libeditor/HTMLEditRules.cpp
@@ -2667,19 +2667,23 @@ HTMLEditRules::WillDeleteSelection(nsIEd
       // Is there a prior node and are they siblings?
       nsCOMPtr<nsINode> stepbrother;
       if (sibling) {
         stepbrother = HTMLEditorRef().GetNextHTMLSibling(sibling);
       }
       // Are they both text nodes?  If so, join them!
       if (startNode == stepbrother && startNode->GetAsText() &&
           sibling->GetAsText()) {
-        EditorDOMPoint pt =
+        EditorDOMPoint pt;
+        nsresult rv =
           JoinNearestEditableNodesWithTransaction(*sibling,
-                                                  *startNode->AsContent());
+                                                  *startNode->AsContent(), &pt);
+        if (NS_WARN_IF(NS_FAILED(rv))) {
+          return rv;
+        }
         if (NS_WARN_IF(!pt.IsSet())) {
           return NS_ERROR_FAILURE;
         }
         // Fix up selection
         ErrorResult error;
         SelectionRef().Collapse(pt, error);
         if (NS_WARN_IF(error.Failed())) {
           return error.StealNSResult();
@@ -3511,18 +3515,22 @@ HTMLEditRules::TryToJoinBlocksWithTransa
   }
   // Do br adjustment.
   nsCOMPtr<Element> brNode =
     CheckForInvisibleBR(*leftBlock, BRLocation::blockEnd);
   EditActionResult ret(NS_OK);
   if (mergeLists || leftBlock->NodeInfo()->NameAtom() ==
                     rightBlock->NodeInfo()->NameAtom()) {
     // Nodes are same type.  merge them.
-    EditorDOMPoint pt =
-      JoinNearestEditableNodesWithTransaction(*leftBlock, *rightBlock);
+    EditorDOMPoint pt;
+    nsresult rv =
+      JoinNearestEditableNodesWithTransaction(*leftBlock, *rightBlock, &pt);
+    if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+      return EditActionIgnored(NS_ERROR_EDITOR_DESTROYED);
+    }
     if (pt.IsSet() && mergeLists) {
       RefPtr<Element> newBlock =
         ConvertListType(rightBlock, existingList, nsGkAtoms::li);
     }
     ret.MarkAsHandled();
   } else {
     // Nodes are dissimilar types.
     ret |= MoveBlock(*leftBlock, *rightBlock, -1, 0);
@@ -8377,82 +8385,102 @@ HTMLEditRules::MaybeSplitAncestorsForIns
                       *pointToInsert.GetChild(),
                       aStartOfDeepestRightNode,
                       SplitAtEdges::eAllowToCreateEmptyContainer);
   NS_WARNING_ASSERTION(splitNodeResult.Succeeded(),
     "Failed to split the node for insert the element");
   return splitNodeResult;
 }
 
-EditorDOMPoint
-HTMLEditRules::JoinNearestEditableNodesWithTransaction(nsIContent& aNodeLeft,
-                                                       nsIContent& aNodeRight)
+nsresult
+HTMLEditRules::JoinNearestEditableNodesWithTransaction(
+                 nsIContent& aNodeLeft,
+                 nsIContent& aNodeRight,
+                 EditorDOMPoint* aNewFirstChildOfRightNode)
 {
   MOZ_ASSERT(IsEditorDataAvailable());
+  MOZ_ASSERT(aNewFirstChildOfRightNode);
 
   // Caller responsible for left and right node being the same type
   nsCOMPtr<nsINode> parent = aNodeLeft.GetParentNode();
   if (NS_WARN_IF(!parent)) {
-    return EditorDOMPoint();
-  }
-  int32_t parOffset = parent->ComputeIndexOf(&aNodeLeft);
+    return NS_ERROR_FAILURE;
+  }
   nsCOMPtr<nsINode> rightParent = aNodeRight.GetParentNode();
 
   // If they don't have the same parent, first move the right node to after the
   // left one
   if (parent != rightParent) {
+    int32_t parOffset = parent->ComputeIndexOf(&aNodeLeft);
     nsresult rv =
       HTMLEditorRef().MoveNodeWithTransaction(
                         aNodeRight, EditorRawDOMPoint(parent, parOffset));
+    if (NS_WARN_IF(!CanHandleEditAction())) {
+      return NS_ERROR_EDITOR_DESTROYED;
+    }
     if (NS_WARN_IF(NS_FAILED(rv))) {
-      return EditorDOMPoint();
+      return rv;
     }
   }
 
   EditorDOMPoint ret(&aNodeRight, aNodeLeft.Length());
 
   // Separate join rules for differing blocks
   if (HTMLEditUtils::IsList(&aNodeLeft) || aNodeLeft.GetAsText()) {
     // For lists, merge shallow (wouldn't want to combine list items)
     nsresult rv =
       HTMLEditorRef().JoinNodesWithTransaction(aNodeLeft, aNodeRight);
+    if (NS_WARN_IF(!CanHandleEditAction())) {
+      return NS_ERROR_EDITOR_DESTROYED;
+    }
     if (NS_WARN_IF(NS_FAILED(rv))) {
-      return EditorDOMPoint();
-    }
-    return ret;
+      return rv;
+    }
+    *aNewFirstChildOfRightNode = Move(ret);
+    return NS_OK;
   }
 
   // Remember the last left child, and first right child
   nsCOMPtr<nsIContent> lastLeft =
     HTMLEditorRef().GetLastEditableChild(aNodeLeft);
   if (NS_WARN_IF(!lastLeft)) {
-    return EditorDOMPoint();
+    return NS_ERROR_FAILURE;
   }
 
   nsCOMPtr<nsIContent> firstRight =
     HTMLEditorRef().GetFirstEditableChild(aNodeRight);
   if (NS_WARN_IF(!firstRight)) {
-    return EditorDOMPoint();
+    return NS_ERROR_FAILURE;
   }
 
   // For list items, divs, etc., merge smart
   nsresult rv = HTMLEditorRef().JoinNodesWithTransaction(aNodeLeft, aNodeRight);
+  if (NS_WARN_IF(!CanHandleEditAction())) {
+    return NS_ERROR_EDITOR_DESTROYED;
+  }
   if (NS_WARN_IF(NS_FAILED(rv))) {
-    return EditorDOMPoint();
+    return rv;
   }
 
   if (lastLeft && firstRight &&
       HTMLEditorRef().AreNodesSameType(lastLeft, firstRight) &&
       (lastLeft->GetAsText() ||
        (lastLeft->IsElement() && firstRight->IsElement() &&
         CSSEditUtils::ElementsSameStyle(lastLeft->AsElement(),
                                         firstRight->AsElement())))) {
-    return JoinNearestEditableNodesWithTransaction(*lastLeft, *firstRight);
-  }
-  return ret;
+    nsresult rv =
+      JoinNearestEditableNodesWithTransaction(*lastLeft, *firstRight,
+                                              aNewFirstChildOfRightNode);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    return NS_OK;
+  }
+  *aNewFirstChildOfRightNode = Move(ret);
+  return NS_OK;
 }
 
 Element*
 HTMLEditRules::GetTopEnclosingMailCite(nsINode& aNode)
 {
   nsCOMPtr<Element> ret;
 
   for (nsCOMPtr<nsINode> node = &aNode; node; node = node->GetParentNode()) {

--- a/editor/libeditor/HTMLEditRules.h
+++ b/editor/libeditor/HTMLEditRules.h
@@ -545,21 +545,23 @@ protected:
    *     The first editable paragraph's content will be moved into the second
    *     editable paragraph and the non-editable paragraph becomes the first
    *     paragraph of the editor.  I don't think that it's expected behavior of
    *     any users...
    *
    * @param aLeftNode   The node which will be removed.
    * @param aRightNode  The node which will be inserted the content of
    *                    aLeftNode.
-   * @return            The point at the first child of aRightNode.
+   * @param aNewFirstChildOfRightNode
+   *                    The point at the first child of aRightNode.
    */
-  EditorDOMPoint
-  JoinNearestEditableNodesWithTransaction(nsIContent& aLeftNode,
-                                          nsIContent& aRightNode);
+  MOZ_MUST_USE nsresult
+  JoinNearestEditableNodesWithTransaction(
+    nsIContent& aLeftNode, nsIContent& aRightNode,
+    EditorDOMPoint* aNewFirstChildOfRightNode);
 
   Element* GetTopEnclosingMailCite(nsINode& aNode);
 
   /**
    * PopListItem() tries to move aListItem outside its parent.  If it's
    * in a middle of a list element, the parent list element is split before
    * aListItem.  Then, moves aListItem to before its parent list element.
    * I.e., moves aListItem between the 2 list elements if original parent