Grill texture map

Render it as a .tif, or .png and it should retain the transparency layer info (for .png you just check the box that says *Include Transparency, and I imagine the same for a .tif). I am not aware of other exporting formats in FF that preserve the transparent parts.

jffe

I have found that getting the result window to show a trans background requires the presence of a image module to be plugged in somewhere in your input path which then replaces the automatic image that gets placed there. You may not even need an image in your result but for whatever reason having the image module plugged in will give you the transparent background
in the result window.

Sometimes I just connect the image module into the second input of a switch while leaving
the first input as its original connection. Then dont even bother putting a control on your switch, the mere presence of the plugged in image model will give the result.

That is what I learned to do thru trial and error, you can try it if you have any trouble with the above solutions.