I'm using the standard release Thunderbird 31.0 All my mail accounts are Pop mail accounts so they are downloaded to the respective mail accounts in Thunderbird on my computer. I have to select an email to read it. i've never known any different. Emails do not auto open without selecting by some method. eg; Next unread message or use arrow keys etc If I delete an email then it will auto select the next email unless you use the 'Deselect on Delete 1.1' addon.

Maybe you have an IMAP mail account? When you subscribe to see folders, only the headers are downloaded, then when you select to read an email, the folder is downloaded to a temp cache to faciltate quicker access. If you synchronize any or all of your subscribed folders then a copy of the folder is downloaded to Thunderbird and you can read these emails even if using offline mode. more info on synchronising:

• https://support.mozilla.org/en-US/kb/imap-synchronization

No, I have a pop3 account. I sure that by hovering over the email in Inbox I could see its contents.

I have solved my problem, I had moved the line that runs across the Inbox page downwards & therefore couldn't see the email. I feel like an idiot, I should have worked it out for myself.....lol