I just upgraded Thunderbird from 68.x to 78.0 (32-bit) in Windows 10. Now the message pane is blank, regardless of whether I select a message. I tried closing and reopening the message pane with F8 but it remained blank. I can now only read messages by double-clicking and opening them in a separate window. When I restarted Thunderbird in safe mode the message pane worked properly. I therefore removed the one add-on I had been using (an English dictionary). However, once I resumed work in normal mode the problem remained. I have since upgraded once more, to the 78.0 64-bit version this time but all is the same: blank message pane unless in safe mode.