According to http://kb.mozillazine.org/Actions_for_attachment_file_types#Unexpected_handling_of_certain_attachments the problem might arise from a corruption of the mimetypes.rdf file in the thunderbird profile. In my case simply deleting this file and hoping that thunderbird will restore it didn't work, though.
According to http:// kb.mozillazine. org/Actions_ for_attachment_ file_types# Unexpected_ handling_ of_certain_ attachments the problem might arise from a corruption of the mimetypes.rdf file in the thunderbird profile. In my case simply deleting this file and hoping that thunderbird will restore it didn't work, though.