You can single click the Mailing List in the address Book window and sort on columns by clicking on Headers. This is display only. It does not affect the Mailing List edit display that shows entries in the order of entry. You cannot change this.

That is my point I want to affect the Mailing List edit display to facilitate ease of entry

It is open source software. You can start programming. I explained how it works.

If you want to facilitate ease of entry then use drag and drop method to put that contact located in the selected address book into the mailing list.

You do not need to do it the long winded way by manually editing the Mailing List via the 'Edit mailinglist name' window. As Airmail has already correctly mentioned and I concur with Airmail, this list will always be listed in the order you actually edit/enter contact.

So, as the contact would have to be in the associated address book anyway and the mailing list is just a select view of specific contacts in that address book; like putting a tag on a group of contacts, use drag and drop method to put contacts in mailing list. Manual input is made available, but it is not the quickest nor easiest method.

Note: if you attempt to put a contact into a Mailing List and it fails, then it is likely that the contact did not have an email address stated in the 'Email' field.

See some helpful info here: https://support.mozilla.org/en-US/kb/how-create-and-use-mailing-lists-thunderbird