Mozilla Firefox before 3.0.13, and 3.5.x before 3.5.2, allows remote attackers to spoof the address bar, and possibly conduct phishing attacks, via a crafted web page that calls window.open with an invalid character in the URL, makes document.write calls to the resulting object, and then calls the stop method during the loading of the error page.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.