In OS X, what causes a crash that shows a transparent black curtain?

Question

I just got a very odd error using my MacBook Pro with Mac OS X Snow Leopard 10.6

I was in Firefox 6.0, trying to enter info in a web form, and a transparent black curtain came down from the top to the bottom of the screen. Then a message popup that said,

You need to restart you computer. Hold down the power button until the computer turns off...

I think I've seen this once before a while ago.

Are there any common causes for this dramatic crash?

Answer 1

This is a kernel panic... see the support site for more info If you think this is scary you should have seen 10.0 and i think early versions of 10.1... it would just dump to the screen so youd get black terminal screen with a ton of binary code.

Answer 2

That's called a kernel panic:

A kernel panic is an action taken by an operating system upon detecting an internal fatal error from which it cannot safely recover. The term is largely specific to Unix and Unix-like systems; for Microsoft Windows operating systems the equivalent term is "Bug check" (or, colloquially, "Blue Screen of Death").

The kernel routines that handle panics (known as panic()) in AT&T-derived and BSD Unix source code) are generally designed to output an error message to the console, dump an image of kernel memory to disk for post-mortem debugging and then either wait for the system to be manually rebooted, or initiate an automatic reboot.1 The information provided is of highly technical nature and aims to assist a system administrator or software developer in diagnosing the problem.