Weak PRNG generator is used to generate temporary files names for XMLHttpRequest. It may be used to access content of local files by creating temporary HTML file with predictable name.
CVE-2007-0801 (The nsExternalAppHandler::SetUpTempFile function in Mozilla Firefox 1.5.0.9 creates temporary files with predictable filenames based on creation time, which allows remote attackers to execute arbitrary web script or HTML via a crafted XMLHttpRequest.)
CVE-2007-0800 (Cross-zone vulnerability in Mozilla Firefox 1.5.0.9 considers blocked popups to have an internal zone origin, which allows user-assisted remote attackers to cross zone restrictions and read arbitrary file:// URIs by convincing a user to show a blocked popup.)
