Hello, Tom and Andy,

A bizarre thing just happened.

I used Ctrl-Alt-F1 to switch to the first VT. When I pressed Ctrl-Alt-F7 to switch back to X, the Unity GUI was displayed.

However, when I opened Firefox and tried to navigate to YouTube, everything went black and I was left with only the mouse cursor.

When I repeat the above steps, I get the same result.

You can view the Xorg.0.log here:

http://pastebin.com/3C1eXXPS

The last line is very interesting:

[ 79.072] PVR:(Fatal): Debug assertion failed! [1785, /sgxtransfer_utils.c]

It's the first thing I've seen that hints at the cause of my problems.