If you try to download a file – let's say test.jpg (Node ID = 112, Object ID = 120) – using Content/Download without the version and file parameter, Firefox (21 - 23) will be saving the file without the extension, using the Object ID for name.

Instead Ex.: http://my_site.com/content/download/112/120/version/1/file/test.jpg
Use Ex.: http://my_site.com/content/download/112/120

Suggested fix:
Use the code below to passe the name to eZFile::downloadHeaders

eZFile::downloadHeaders( $fileName, self::dispositionType( $fileInfo['mime_type'] ) === 'attachment',
( $fileInfo['filename'] != "" )? $fileInfo['filename'] : false, $fileOffset, $contentLength, $fileSize );