This is a user style sheet to do what it can to avoid clickjacking.

Clickjacking or, more formally, user interface redressing, is a
class of web-based security vulnerabilities similar to phishing
scams. The technique uses web standards to trick unsuspecting
victims into performing actions they were not intending to. A
dramatic demo can be seen at

    http://www.planb-security.net/notclickjacking/iframetrick.html

The clickjane.css file is a user style sheet that does its best
to ensure that any possible clickjacking attempts are immediately
visible instead of remaining invisible.