Ubuntu crashes (shut downs automatically) when browsing the Web

[Jet]

When I load two or more pages, Ubuntu shutdowns automatically. The
browser is Mozilla Firefox. I think this is a bug. I report it to
Launchpad as a bug. I don't know how this happens. I may think it's
the LiveCD instill who made this bug because the LiveCD crashes when I
load pages too much on Mozilla Firefox. It may be a bug with the Linux
kernel.