--- firefox-79.0/parser/expat/lib/xmlparse.c.cve-2022-43680	2022-11-18 10:00:58.441551281 +0800
+++ firefox-79.0/parser/expat/lib/xmlparse.c	2022-11-18 10:05:30.523029488 +0800
@@ -1004,6 +1004,14 @@ parserCreate(const XML_Char *encodingNam
   parserInit(parser, encodingName);
 
   if (encodingName && !protocolEncodingName) {
+    if (dtd) {
+      // We need to stop the upcoming call to XML_ParserFree from happily
+      // destroying parser->m_dtd because the DTD is shared with the parent
+      // parser and the only guard that keeps XML_ParserFree from destroying
+      // parser->m_dtd is parser->m_isParamEntity but it will be set to
+      // XML_TRUE only later in XML_ExternalEntityParserCreate (or not at all).
+      parser->m_dtd = NULL;
+    }
     XML_ParserFree(parser);
     return NULL;
   }