I am using Ubuntu 14.04, and recently have a problem with Thunderbird: Some pdf files attached to emails are not treated as pdf files should be.
The attachment settings option for pdf's is set to automatically open pdf files with the document viewer. This works for some (most) pdf's files in attachments. However, for some files, a dialogue opens and asks what to do for the attachment, and suggests to open it with the video player. If I instead save the attachment to some folder, it is correctly recognized as a pdf and opened with the correct automatic program.
Where does this come from, and how can I fix it?
Edit: I checked the email source which states this:
Content-Type: video/x-flv; name="Erhebung.pdf" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="Erhebung.pdf"
apparently, the content type is wrongly recognized