Thanks, Craig. I'm also mainly a Mac user, and the behavior in Safari for me is exactly as you describe – for recent attachments only. Those uploaded on 11/6 or earlier open in a new Safari tab. It looks like we've been trying the same things, except that I had not tested it with Explorer. I get the same result with PNGs, so this is not specific to PDFs. On a website that I manage, PDFs are behaving as they always have in Chrome.