A bug in Firefox that was first reported 12 years ago is still being exploited by malicious websites. The bug essentially allows a malicious site to ensnare a user by repeatedly showing them an “Authentication Required” pop-up login box. When the users tries to close the login box, a new one appears. The only way out is to close the browser.

Users

Source: Hot Hardware – Firefox Users Under Attack By 12-Year-Old Bug Exploited By Malicious Sites