Saving ".cgi" image

I'm playing this web game that displays an image after you unlock a different achievement, so to speak, but the image is shown as part of a cgi script, i.e., "http://blahblah.blah/show.cgi?target=x".  On Firefox in Ubuntu, I can't save the image; I end up with a 500 Internal Server error page that gets saved to my computer instead.  Any tips?

Probably an intentional misconfiguration of the server to prevent you from saving the image. You can always make a screenshot and save it as .png. Then you'll have a copy of the image but not the original image file, so to speak. If you want the original, dunno.

Probably a misconfiguration on your end, too. It means the image isn't getting cached, so it's trying to reload it when you try to save it, which the server then craps out on.