You must now install the “x11proto-xf86dri-dev” package for this to work. I don’t know why. Please message me if you know the cause of this.

Let me pepper this with keywords in the hopes that someone won’t have to spend as much time searching for this as I did:

Xlib: extension "XFree86-DRI" missing on display ":0.0"
ATI fglrx DRI radeon X1400
ATI Radeon Linux Driver Proprietary Xorg

Ok. Now that’s done, here’s the fix. Took me a week to find this, but it seems to work fine now:

  1. sudo apt-get install fglrx
  2. aticonfig –initial
  3. Edit xorg.conf, add the following lines:

    Section "Extensions"
    Option "Composite" "disable"

Now it works!