When you compose an email with Thunderbird (all versions) and hit SEND, the compose window will remain open until the email is sent. This is annoying, especially when you’re sending big attachments.
I wanted the compose window to disappear as soon as possible since Thunderbird will warn me if there is an error anyway.
So Click Edit/Preferences/Advanced and select the General tab. Click the Config Editor button and accept the warning (which should really be removed, it is worthless). In the Filter box enter ‘sendinback’ which will filter the list so that only
mailnews.sendInBackground will be visible. Double click it so the boolean Value becomes ‘true’.
Restart thunderbird. Now when you click send after composing an email, the Compose Window will disappear as soon as possible (still not as soon as I’d like).
For google:
How to disable the compose window. How to hide the compose window. How to make the compose window disappear. Thunderbird. Shredder.
Cheers.