I tried to install Thunderbird, and ran the installation program called Setup. The intalllation hung up at some point, and the progress bar did not move for several hours. I decided to cancel the installation and try again. Clicking the red X box on the install frame did nothing. I went into Task Manger > Processes > End process. The process did not end, but Processes greyed out, I inferred inoperative. So I performed a hard stop. When I restarted, it appeared that Tb had installed. However some incoming mail was placed at the top of the Inbox list, and other items were placed at the bottom. I suspect this bizarre sequence was caused by a bug, which I would like to report I am running Windows 7 on a machine with ample resources.