In Mozilla Thunderbird, B and F can be used to move up and down, respectively, in the thread pane. What are their counterparts for moving up and down in the folder pane?
There aren't any built in keyboard shortcuts to do this directly.
The keyboard shortcuts available by default in Thunderbird are listed in this documentation.
Indirectly, you can press the keyboard shortcut for "Move to Next Mail Pane": F6 (which switches your keyboard focus between the visible mail panes) until the Folder pane is focused, then use the Up ↑ and Down ↓ arrow keys to move between folders.
If you really want a direct keyboard shortcut that always does exactly this function, you could install Dorando Keyconfig, add a new key, and write custom code to do what you want, but this seems like overkill to me when there is a simple, albeit indirect, method already available.