--- a/editor/libeditor/HTMLEditRules.cpp
+++ b/editor/libeditor/HTMLEditRules.cpp
@@ -4326,18 +4326,22 @@ HTMLEditRules::WillOutdent(Selection& aS
     bool curBlockQuoteIsIndentedWithCSS = false;
     for (uint32_t i = 0; i < arrayOfNodes.Length(); i++) {
       if (!arrayOfNodes[i]->IsContent()) {
         continue;
       }
       OwningNonNull<nsIContent> curNode = *arrayOfNodes[i]->AsContent();
 
       // Here's where we actually figure out what to do
-      nsCOMPtr<nsINode> curParent = curNode->GetParentNode();
-      int32_t offset = curParent ? curParent->IndexOf(curNode) : -1;
+      int32_t offset;
+      nsCOMPtr<nsINode> curParent =
+        EditorBase::GetNodeLocation(curNode, &offset);
+      if (!curParent) {
+        continue;
+      }
 
       // Is it a blockquote?
       if (curNode->IsHTMLElement(nsGkAtoms::blockquote)) {
         // If it is a blockquote, remove it.  So we need to finish up dealng
         // with any curBlockQuote first.
         if (curBlockQuote) {
           rv = OutdentPartOfBlock(*curBlockQuote, *firstBQChild, *lastBQChild,
                                   curBlockQuoteIsIndentedWithCSS,