Enabling extension Composite makes firefox crash when accesing certain sites
such as:

www.cnn.com
www.theregister.co.uk
www.shockwave.com

If I disable Composite from /etc/X11/xorg.conf and restart the xserver firefox
works fine and those pages can be accessed normally.

To reproduce just enable Composite in /etc/X11/xorg.conf
Running firefox from a terminal produces the following output:

-------- begin of output -----------
The program 'Gecko' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
  (Details: serial 85 error_code 8 request_code 144 minor_code 3)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)
-------- end of ouput -----------

The machine is a Pentium M laptop with an Intel 855GM card. I'm running gentoo
with kernel 2.6.8.1 (development-sources-2.6.8.1). I also tryed kernel 2.6.7
(gentoo-dev-sources-2.6.7-r13) and the problem persists.
Both kernels are using i915 driver for DRM. Obtained from patch:
(http://www.skynet.ie/~airlied/patches/dri/i915_linux.diff)