Thank-you, thundergnat, for the remarks on Net::Netrc.

I e-mailed Graham Barr directly, and he kindly gave a fast response, saying I should connect thru a firewall like this:

my $ftp = Net::FTP->new( $firewall_host, Firewall => undef );

$ftp->login(
    "$ftp_user\@$ftp_host $proxy_user",
    $ftp_password,
    $proxy_password
);
[download]

I tried this and it works just fine.

I copied Graham's solution to this thread in case it helps other seekers of wisdom.

I'll watch Net::Config in case Graham enhances it to handle this new firewall type. But in the meantime, his quick solution is just the ticket.