Thunderbird by default opens just like you closed it. The normal cause in changing this behavior is when users install software like CCleaner that thinks it knows best and deletes the setting file. Are you using anything like that?

I do not have CCleaner on my PC but poblem still persists.

Thunderbird creates a file called session.json when Thunderbird is closed. This retains the layout as is when closed. It refers to this the next time Thunderbird opens and then it deletes the file. Something on your computer is deleting that file. You just need to figure out what it is.

Here is what Thunderbird says about that file.

Default windows layout. This includes data on what tabs are open. Thunderbird (3.0 and later) deletes this file after reading the settings. Its re-created and the layout saved when Thunderbird terminates normally.

Thanks for your help. I found the file. It is not being deleted and problem still exists.

a) When I open TB - and it opens minimized to a corner of the screen where I always keep it open unless I want to look at new mail - and go to view/layout, only Folder Pane is ticked. I can then open TB and it displays the page with Email, Accounts & Advanced Features (don't know what it's called), and go to View/Layout again, only Folder Pane is ticked. But as soon as I open Inbox to display my mails, Message pane gets ticked and it's back!!!

So I untick Folder Pane or press F8 or drag the slider down and the Message Pane has gone. I click on the X to close TH.

b) Go to a)

Since you mentioned that it sometimes opens to the Email, Accounts and Advanced Features page that seems to be and indicator of a bad upgrade issue. I found this solution that you might want to try. It can't hurt.

There is currently a problem with the update process.

On the toolbar then Add-ons Select extensions and remove the Lightning (calendar) addon Restart Thunderbird Reinstall Lightning/calendar addon - if you need the functionality Please tell us, does that help?

I don't have Lightning/Calender add on. The only add ons I have are:

Adblock Plus 2.7 CompactHeader 2.1.0 Folderpane Tools 0.6.1 Use Bcc Instead 3.4.1

The only Addon I remember Installing was Adblock Plus. I don't use the others, so I deleted all of them except Adblock Plus. One of them must have been causing the problem because it now appears to have been resolved and the Accounts & Advanced Features page no longer appears. TB opens directly with the Inbox page, which is what I always wanted but never knew how to achieve. Thank you very much for your help

I'd suspect folderpane tools

Your welcome. If you have time to test Wayne's theory to see if that is the problem add on please report back. It might help the next person.

kologha, what were you able to determine?

Hi, I have not had the opportunity to test which of the addons was causing the problem. The main thing is that the problem has gone. Thanks very much for all your help.

I have this problem and I do run Ccleaner. I saw in another message that Thunderbird creates a file called session.json which it uses to remember settings from session to session. Ccleaner deletes this file so Thunderbird doesn't remember that you want message pane off.

I told Ccleaner to exclude this file. I closed Thunderbird, I ran Ccleaner, and then I reopened Thunderbird and the message pane was gone.

For those of you who wish to use Ccleaner & Thunderbird this seems to fix the F8 message pane issue.