One more thing: I'm using the dark view.

What OS are you using?

Can you post an image so we can see what you are seeing ?

If you restart Thunderbird in Safe Mode do you still get the same problem ? https://support.mozilla.org/en-US/kb/safe-mode-thunderbird

TRy this: In Thunderbird

• 'Help ' > 'TRoubleshooting Information'
• Click on 'Open Folder' button

A new window opens showing the contents of you 'profile name' folder.

• Exit Thunderbird now.

Delete the following files:

• session.json
• xulstore.json

Start Thunderbird

Please report back on results.

I restarted in Safe mode as suggested and the problem went away. I then disabled gContactSync and the problem is gone. I had a blank area where the header (From, Subject, To, etc.) should be.

Many thanks for the feedback. Addons can do all kinds of weirdness on occasions, but this is a new one.

It might be worth uninstalling the addon and then trying a fresh updated version. https://addons.thunderbird.net/en-US/thunderbird/addon/gcontactsync/

I'm only using the Provider for Google Calendar addon.

Many thanks for your help. I've removed gContactSync and added the updated version as suggested. All seems OK. To answer your earlier question, I'm running Windows 10 Pro 64-bit, although I only seem to get 32-bit Thunderbird.