User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:62.0) Gecko/20100101 Firefox/62.0 Build ID: 20180806191531 Steps to reproduce: Specific version 52.9.1, 32-bit build running on Windows 7 Enterprise 64-bit. It can take several minutes to download a new message from my mail server when it is being remotely accessed over the Internet. Server runs Dovecot version 1:1.2.15-7+deb6u1 (package from Debian squeeze). I'm hoping that when I replace that server with one that has more memory and a much newer Dovecot release, that this extreme slowness will be fixed. If it's not, I may open another bug for that. These problems do not happen when I am at home, where the connection from Thunderbird to the server is over a LAN rather than the Internet. Frequently I will give up waiting when it takes too long, click on another of my mail folders, and read messages that have already been downloaded. The problem is that Thunderbird hasn't forgotten about the message download that I gave up waiting for ... and once the download is successful, whatever message I am looking at will be replaced by that message, even if I have moved on to a completely different folder. Actual results: The display in the reading pane gets replaced with a message that I attempted to download minutes earlier. Expected results: It's fine for Thunderbird to complete the background download of a message when I give up waiting, but it should not take over the reading pane to show me that message when I have begun looking at other messages.