Messages I receive when opened have buttons at the top labeled "Reply", "Reply All", and "Forward", and attachments if any at the bottom.. (1) Clicking or shift-clicking "Reply" opens a new window with the original message and the sender in the "To" field, with the format either HTML or plain text, as expected. If instead I click the down arrow by the Reply button it opens a drop-down menu with "Reply in HTML" and "Reply in plain text" as choices. No matter which I choose, nothing happens - no new window opens. Clicking either "Reply All" or its down arrow does the same thing: opens a drop down menu with the same two choices as with Reply. Again, no matter which I choose, nothing happens. If instead I go to the menu, click Messages and from the drop-down menu click or shift-click either Reply or Reply to all, it *does* work as expected. (2) If an attachment is *.mov and I click it, a window opens asking what I should do with the file, and everything works as expected. If an attachment is *.jpg, then clicking it does nothing; double-clicking it does nothing. Right-clicking it opens a menu with the first choice being "Open". If I click that nothing happens. The only way I can open the attachment is to save it, then open the saved file. I'm running the latest (91.6.1) version of Thunderbird under Windows 10. Does anyone know what is wrong? Thanks!