I am running the latest Thunderbird 78 on Mac Big Sur. All the folders are showing ok, and I can read emails, BUT when I click on an email in the email listing top right, it turns completely blank. I can still click on the blank space and read the email. If I then click on another email in the listing, the original one returns to normal. I have a feeling it is a font/colour setting somewhere; as if the 'active' email changes colour, foreground and background colours change to the same colour when the item is clicked? Any ideas would be appreciated. Barry