This seems to be linked to: (A) Opening your Yahoo! mail inbox from another Yahoo! page, and (B) Downloading an attachment Some time after downloading the attachment, a script in the page tries to close it. Normally, that's not allowed, but when the page was opened using a link from Yahoo! itself, it seems to be allowed. Try starting a new Yahoo! mail tab by pasting https://mail.yahoo.com/ in the address bar and pressing Enter to load your inbox that way. It should be more resistant to closing itself.