Security researcher Mariusz Mlynski reported that an attacker able to convince a potential victim to set a new home page by dragging a link to the "home" button can set that user's home page to a javascript: URL. Once this is done the attacker's page can cause repeated crashes of the browser, eventually getting the script URL loaded in the privileged about:sessionrestore context.

Reference:
http://www.mozilla.org/security/announce/2012/mfsa2012-16.html