Can you post a screenshot if you don't mind?
I know that would be a bit of work, since you would have to cover up a lot of personal stuff in such a screenshot.
Unify your POP email accounts with a global inbox | Thunderbird Help
We'll show you how to merge inboxes from various POP accounts to make what is called a global inbox, where all of the mail can be displayed in one place.

Step 6 is a UX nightmare LOL.