[eluser]dootzky[/eluser]
for me, FF 6.0 in Windows is giving me this mime type: "application/octet-stream", so just put this as well in your /config/mimes.php config file, and you're good to go.
kinda sucks, but it works
Code:
'pdf' => array('application/pdf', 'application/x-download', 'application/octet-stream'),