I have recently upgraded to MAC Sierra. Thunderbird has become useless because of extremely poor performance. It takes ten minutes to get rid of the circling icon, and then, if I do even a very small task (enter text in an email, for example, after just a few key strokes it once again goes to a circling icon that last sometimes 10 minutes or more. I do have large files, but the vast majority of my emails have been moved to archived files and are not online. I also have several email accounts. Thunderbird has been deteriorating over the yearas, but with MAC Sierra it has, essentially, become useless. I suspect I need phone or chat to do a decent job of troubleshooting my problems. Any suggestions. Thanx.