the Firesign Theatre filmed a stage show at CBS studios in Los Angeles for a PBS special titled "Weirdly Cool".
The Firesign Theatre PBS special was shown on
many PBS stations that December.
Here is an article about the making of the special.
Here's a flash panorama showing them after recording "Weirdly Cool"
Phil Proctor has a number of backstage shots from "Weirdly Cool" here.
A couple of large posed shots (about 240k each)
of Firesign Theatre as the Nick Danger cast
here and here,
plus a collage of miscellaneous smaller photos.