I have the same problem at home and at work on many computers. I have seen it where the .pdf file opens fine (either as a new tab in Thunderbird, or as a file in my default .pdf reader, or as a saved file) then later the same day I get a blank screen (and saving it results in a 1KB file with garbage in it). Moving or copying the email with the attachment to a different folder SOMETIMES works and sometime not (on EXACTLY the same Email). For example while in the INBOX the .pdf file was opening but when I the email was moved to a subfolder the problem occurred. Moving the Email back to the INBOX fixed it once but when I repeated the steps it failed. If I forward the email to another account and open the email in a non-Thunderbird program the .pdf attachment opens fine. In other words, this is an intermittent problem. All these problems started when Thunderbird added the ability to view a .pdf file within Thunderbird (as a new tab).