I cannot open PDF attachment on my Mac. One might think it is just slow, but the attachment never comes up. I have to copy the PDF address and paste it into Safari or Explorer, which have no trouble opening the very PDF that Firefox would not handle. I am guessing that I have some setting that is barring PDFs; other attachments open fine. My adobe is up to date, I think; if that was the problem Safari, too, would not be able to open the PDF.