Thunderbird present a "compact folder" message (done many time over the years), so I said go ahead. My Inbox was "cleared" showing "no messages" icon. First, this realy is a SCARY thing to show when compacting a folder, but they normally all come back. You really should display some different message or show the message still there while compacting. This time I got an error (sorry I did not save the exact error message) but it was that the folder could not be compacted due to an error, possibly not enough disk space and to check and make more space available. I had 290GB free space on my C: drive where Thunderbird is installed in the standard "Program Files" folder. After dismissing the error, my Inbox still displayed "No Messages" - THIS is the BUG that needs fixing. I thought I had lost all my emails! Fortunately, exiting Thurderbird and reboot my Laptop and restarting Thunderbird shows the Inbos with all its expected messages. I don't know how to report a bug formally, so I am hoping someone that does can pass this along to the appropriate peope or file it in the appropriate bug reporting system.