mhshow/firefox can't find file

Hi,

On ~/.mh_profile I have (among other settings):

  Folder-Protect: 700
  Msg-Protect: 600
  Path: mail
  mhshow: -noheader -notextonly -noinlineonly -noconcat
  mhshow-show-text/html: firefox %f
  moreproc: less

When I run:
  mhshow +inbox <msg-number>

I get, piped through less:

  Date:    Thu, 05 Nov 2020 08:45:59 +0000
  To:      <the To: address line>
  From:    <the From: address line>
  Subject: <the Subject: address line>

Followed by one blank line,
Then almost all the lines in the header,
except the ones that start with:
   Received:
   Message-ID:
the ones printed above, i.e.
   Date
   To
   From
   Subject
and these two:
  Content-Transfer-Encoding: quoted-printable
  Content-Type: text/html; charset=UTF-8

When less exits, firefox open an error page with:

  File not found
  Firefox can’t find the file at <Path from ~/.mh_profile>/mhshowpMnlWx.html.

    Check the file name for capitalization or other typing errors.
    Check to see if the file was moved, renamed or deleted.

This used to work long ago with mhn. If I now run
(depecrated) mhn, I get:

The same output piped through less
When less exits, the message body, which is text/html is
sent as is through less, showing a file
  <Path from ~/.mh_profile>mhnx8lFiR 

What setting am I missing, or maybe incorrect, to have
mhshow work?

Also why, with the -noheader option, I still get the header?

Thanks,

-- Henrique