firefox md5 fails, why?

[alexander villalba <alexvillalb159@gmail.com>]

initially posted this in a firefox forum but received no answer:
 https://www.mozilla-hispano.org/foro/viewtopic.php?f=2&t=11923


 Greetings!:

 I went to:

  ftp://mozilla.c3sl.ufpr.br/mozilla/rele ... ses/7.0.1 /

 download files:

 md5sum
 md5sum.asc

 having no public key firefox download it:

 gpg - recv-keys C52175E2 (from hkp: / / pgp.mit.edu: 11371)

 and check the digital signature:

 gpg - verify md5sum.asc

 says it was invalid

 I hope someone can explain.