Extracting an image from a running Flash SWF file?

Is there a way to extract an raw image file from a SWF file that is already running in a browser?

I have had limited success by installing FlashFirebug (Firefox 14.0.1) and then doing the following:

1. use "Inspector" to select the Bitmap a tree hierarchy of objects
2. click on all extraneous objects and drag'n'drop them out of view
3. take a screen shot

Does anyone know a proper way to export the original image file?