On first screenshot (with the select to add account) can you go a menu down as the selection is and save a screenshot with what is at "server settings" for that existing email?

ok, i'll try. attached are two new screenshots with (i hope) the info you need.

I probably was unclear - would you make a screenshot with what it's already set on your side on that account on "server settings"? Attached your picture back and I've marked with green the menu which should be selected.

First, change the Account Name to something other than the email address, e.g. EarthlinkIMAP, copy the existing Inbox mail to Local Folders, then restart TB and add the account as POP:

http://kb.mozillazine.org/Convert_a_POP_account_to_a_IMAP_account

If you know the server settings, go offline from File/Offline/Work Offline, add the POP account, click Manual config., enter the details, and click Advanced config. to set all the other parameters, then finally go back online. If you don't do this, the default POP settings may download the Inbox and delete the messages from the server, (which may not be what you want).