Last time I tried to download the non-free firmware and put it on
another USB disk, I ended up in changing to a shell from the installer
and unpacking the firmware blobs to the correct place manually because
I wasn't able to figure out how the layout on the firmware disk had to
be for the installer to find it.
Because the docs are so vague about that and the installer didn't
bother to log the path it was looking at to any log that I was able to
find.
And yes, I am a DD and should be able to figure that out.