Mozilla Firefox before 2.0.0.5 does not prevent use of document.write to replace an IFRAME (1) during the load stage or (2) in the case of an about:blank frame, which allows remote attackers to display arbitrary HTML or execute certain JavaScript code, as demonstrated by code that intercepts keystroke values from window.event, aka the "promiscuous IFRAME access bug," a related issue to CVE-2006-4568.