var doc = document.implementation.createHTMLDocument('a'); Node's can cache nodelists in m_nodeLists. They keep a counter on their document, via document()->addNodeListCache and document()->removeNodeListCache. However, when a node is adopted between documents, nothing is done to keep this balance. On adoption, we should be clearing m_nodeLists and calling document()->removeNodeListCache. var b = document.createElement('b'); // Give it a node list cache on document b.childNodes; // Attach it to doc to update m_document doc.adoptNode(b); doc.body.appendChild(b); doc.body.removeChild(b); // GC here if you can, or reload the page to fire ~Node and cleanup m_nodeLists