From Mozillazine:

The folder pane is the pane at the left. It normally lists your accounts and folders. The thread pane on the right normally lists the contents of the folder. If the folder pane is shown but is empty, see Empty folder pane.

If you don't see a folder pane it is probably because you inadvertently closed (collapsed) it (Bug 340982). To bring it back, just move your cursor to the far left side of the window until the cursor changes into a double-headed arrow (↔), and then drag the splitter bar to the right. Mozilla Suite users can just click on the "grippy" in the middle of the bar at the left edge of the window.

Can you confirm if either of the above matchyour problem?

Great! Worked like a charm...Thank You Mozillazine.

Hello,

I am glad to hear that your problem has been resolved, thank you for marking the answer that solved the problem as such. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support!

I too have this problem, and I'm afraid the recommended solution ("just move your cursor to the far left side of the window until the cursor changes into a double-headed arrow (↔), and then drag the splitter bar to the right") isn't working for me - when I get the double-headed arrow, it just moves the whole window back and forth. Please help!

(NB. I've tried downloading the latest version of Thunderbird, but it automatically started it up without the folder pane, and I've tried starting in safe mode, with the same result.)

Stevencave, Now you post to someone else's thread when you have two of your own, both with answers. Stop wasting peoples time with duplicate posts if you cannot be bothered to read the help already provided to you.