FTP: Firefox can list, Explorer cannot

I cannot get directory listing when logged in to my FTP server using
Internet Explorer, but I can get directory listing Firefox or Filezilla.

Here is my setup:

FTP client (home) <-> Westell router <-> m0n0wall (office) <-> FTP
server.

- For FTP client, I used Firefox and Filezilla, both work, but neither
IE 6 nor IE 8 work.

- The Westell router in my house has no setting to block outgoing
connections

- m0n0wall in the office has 1 public IP address on the WAN side, and
does Inbound NAT to the machine running the FTP server

- The FTP server is pure-ftpd-1.0.29 running on FreeBSD 8.0-STABLE.

When I connect using Firefox, this is what /var/log/xferlog shows:

Aug  1 16:32:44 snail pure-ftpd[71260]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] New connection from
pool-72-95-209-5.pitbpa.east.verizon.net

Aug  1 16:32:44 snail pure-ftpd[71260]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [user]
[anonymous]

Aug  1 16:32:44 snail pure-ftpd[71260]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [pass] [<*>]

Aug  1 16:32:49 snail pure-ftpd[71260]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [WARNING] Authentication
failed for user [anonymous]

Aug  1 16:32:49 snail pure-ftpd[71260]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] Logout.

Aug  1 16:32:50 snail pure-ftpd[71262]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] New connection from
pool-72-95-209-5.pitbpa.east.verizon.net

Aug  1 16:32:59 snail pure-ftpd[71262]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [user] [user]

Aug  1 16:32:59 snail pure-ftpd[71262]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [pass] [<*>]

Aug  1 16:32:59 snail pure-ftpd[71262]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] user is now logged in

Aug  1 16:32:59 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [syst]
[]

Aug  1 16:32:59 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [pwd] []

Aug  1 16:33:00 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [type]
[I]

Aug  1 16:33:00 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [pasv]
[]

Aug  1 16:33:00 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [size]
[/]

Aug  1 16:33:00 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [mdtm]
[/]

Aug  1 16:33:00 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [retr]
[/]

Aug  1 16:33:01 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [pasv]
[]

Aug  1 16:33:01 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [cwd]
[/]

Aug  1 16:33:01 snail pure-ftpd[71262]:
([email protected]) [DEBUG] Command [list]
[]

However, when I connect with Explorer, it never issues a list command:

Aug  1 16:40:01 snail pure-ftpd[71280]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] New connection from
pool-72-95-209-5.pitbpa.east.verizon.net

Aug  1 16:40:01 snail pure-ftpd[71280]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [user]
[anonymous]

Aug  1 16:40:01 snail pure-ftpd[71280]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [pass] [<*>]

Aug  1 16:40:05 snail pure-ftpd[71280]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [WARNING] Authentication
failed for user [anonymous]

Aug  1 16:40:05 snail pure-ftpd[71280]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] Logout.

Aug  1 16:40:12 snail pure-ftpd[71282]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] New connection from
pool-72-95-209-5.pitbpa.east.verizon.net

Aug  1 16:40:12 snail pure-ftpd[71282]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [user] [user]

Aug  1 16:40:13 snail pure-ftpd[71282]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [pass] [<*>]

Aug  1 16:40:13 snail pure-ftpd[71282]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] user is now logged in

Aug  1 16:40:13 snail pure-ftpd[71282]:
([email protected]) [DEBUG] Command [opts]
[utf8 on] 

Aug  1 16:40:13 snail pure-ftpd[71282]:
([email protected]) [DEBUG] Command [syst]
[]

Aug  1 16:40:13 snail pure-ftpd[71282]:
([email protected]) [DEBUG] Command [site]
[help]

Aug  1 16:40:13 snail pure-ftpd[71282]:
([email protected]) [DEBUG] Command [pwd] []

Aug  1 16:40:14 snail pure-ftpd[71284]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] New connection from
pool-72-95-209-5.pitbpa.east.verizon.net

Aug  1 16:40:14 snail pure-ftpd[71284]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [user] [user]

Aug  1 16:40:14 snail pure-ftpd[71284]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [DEBUG] Command [pass] [<*>]

Aug  1 16:40:14 snail pure-ftpd[71284]: (?
@pool-72-95-209-5.pitbpa.east.verizon.net) [INFO] user is now logged in

Aug  1 16:40:14 snail pure-ftpd[71284]:
([email protected]) [DEBUG] Command [opts]
[utf8 on] 

Aug  1 16:40:15 snail pure-ftpd[71284]:
([email protected]) [DEBUG] Command [syst]
[]

Aug  1 16:40:15 snail pure-ftpd[71284]:
([email protected]) [DEBUG] Command [site]
[help]

Aug  1 16:40:15 snail pure-ftpd[71284]:
([email protected]) [DEBUG] Command [pwd] []

Aug  1 16:40:15 snail pure-ftpd[71284]:
([email protected]) [DEBUG] Command [type]
[A] 

Aug  1 16:40:15 snail pure-ftpd[71284]:
([email protected]) [DEBUG] Command [pasv]
[]

Instead, it gives the error message "An error occurred opening that
folder on the FTP server. Make sure you have permission to access that
folder"

Internet Explorer does show the directory listing when I connect from
within the LAN to the FTP server:

[...]

Aug  1 16:53:07 snail pure-ftpd[71314]: ([email protected]) [DEBUG]
Command [pwd] []

Aug  1 16:53:07 snail pure-ftpd[71314]: ([email protected]) [DEBUG]
Command [type] [A]

Aug  1 16:53:07 snail pure-ftpd[71314]: ([email protected]) [DEBUG]
Command [pasv] []

Aug  1 16:53:07 snail pure-ftpd[71314]: ([email protected]) [DEBUG]
Command [list] []

So, it appears that Internet Explorer doesn't like something about the
NAT/firewall setup (?)

Would you please help?

-- 
Janos Dohanics
<[email protected]>