Bug report?

I think I have found a bug. In Firefox, when I choose to “clear all history” it immediatley shuts my computer off, every time. Any ideas?

What versions you have for Firefox, KDE, Netrunner?

everything is all up to date. Netrunner 12.12.1
Firefox 20
[hr]

KDE 4.10.2

I have no idea how to sniff this problem out.