When I have Thunderbird minimized and am working on something else, I will get a notification window that pops up when a get a new email. I used to be able to close this notification window, but in the last month, the "close" button doesn't work anymore. It pops up, covers something I'm doing, and I can't move it or close it. I just have to wait until it disappears. I still want notifications, but they pop up during a game where I only have so many seconds to do something. How can I be able to close the notification box?