I looked a bit at the issue, and what we need is:

• Get a picture/bitmap/screenshot of what is currently being displayed in the plugin.
• A way to convert the obtained image to postscript

The idea is that the postscript data is written to a given filedescriptor, though only on *nix, windows and MAC works differently (how exactly is unknown/ignored for now).

Another link to the plugin API: http://developer.mozilla.org/en/docs/Gecko_Plugin_API_Reference

When I print a page from Firefox (via CUPS) of a web page containing some Flash elements, the areas being rendered by Gnash come out blank, as white space. The rest of the page (non-Flash areas) prints fine.

I'm using the 0.7.2 package with the opengl renderer from Debian unstable, on 64 Studio 1.0 distro, AMD64 dual processor machine, 

daniel@64studio:~$ gnash --version
Gnash 0.7.2
Copyright (C) 2006 Free Software Foundation, Inc.
Gnash comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of Gnash under the terms of the GNU General
Public License.  For more information, see the file named COPYING.
Build options 0.7.2
   Renderer: opengl   GUI: gtk   Sound handler: sdl   Decoder: mad
daniel@64studio:~$ uname -a
Linux 64studio 2.6.17-1-multimedia-amd64-k8-smp #1 SMP PREEMPT Wed Jul 19 12:43: 36 UTC 2006 x86_64 GNU/Linux
daniel@64studio:~$ glxinfo | egrep "(version|vendor)"
server glx vendor string: SGI
server glx version string: 1.2
client glx vendor string: SGI
client glx version string: 1.4
GLX version: 1.2
OpenGL vendor string: VA Linux Systems Inc.
OpenGL version string: 1.2 Mesa 6.5.1
glu version: 1.3