do you have more than one tab open? try right clicking the tab you are on and choosing close all others from the menu. That will leave the home tab and whatever you are currently on open.

This doesn't help me. I have only a single tab open. It's a tab for one of my Local Folders. I can't get from there to my Inbox -- or to any of my other Local Folders.

Further note: Rebooting doesn't help. After doing so and starting Thunderbird, rather than taking me to my Inbox as it normally would, it takes me to the Local Folder that it's stuck in.

I fixed this problem. I found that there are options under View --> Layout. I saw an option "Folder Pane" . When I checked that, the Inbox and all the folders immediately appeared.

  Maybe I'd done something to unset that option? 
  Anyway, it's now working.