If the url works from the firefox browser (or another), but not from the LWP browser, then it must be because of prejudice (cookies, referrer, headers)

use LWP::Simple qw' get $ua ';
$ua->add_handler( "request_send",  sub { shift->dump; return });
get('http://example.com/');
__END__
GET http://example.com/
User-Agent: LWP::Simple/6.00 libwww-perl/6.05

(no content)
GET http://www.iana.org/domains/example/
User-Agent: LWP::Simple/6.00 libwww-perl/6.05

(no content)
GET http://www.iana.org/domains/example
User-Agent: LWP::Simple/6.00 libwww-perl/6.05

(no content)
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