Mozilla Firefox 1.5.0.2, when designMode is enabled, allows remote attackers to cause a denial of service and possibly execute arbitrary code via certain Javascript that is not properly handled by the contentWindow.focus method in an iframe, which causes a reference to a deleted controller context object.  NOTE: this was originally claimed to be a buffer overflow in (1) js320.dll and (2) xpcom_core.dll, but the vendor disputes this claim.