The site you link to is not the current one. https://addons.thunderbird.net/en-US/thunderbird/addon/manually-sort-folders/

Try following the install an add-on instructions. https://support.mozilla.org/en-US/kb/installing-addon-thunderbird#thunderbird:mac:tb60

Thanks. Strangely, when I copied the entire file name manually_sort_folders-1.1.1-tb.xpi it was not found, When I keyed manually it was found immediately.

This is not quite what I am after. I want to move the accounts, me@gmail.com, me@yahoo.com, etc. Some are no longer in use, but I want to keep them, and the bottom of the list is best so the current ones are more easy to spot at the top. Is there an add-on for this?

Read the add on description.

This extension allows you to manually sort (order) your folders in the folder pane of Thunderbird or automatically sort them, but in a better way. This extension also allows you to re-order accounts in the folder pane.

Thanks. The tabs at the top of this window are like many others - small thin grey typeface on a grey background, very hard to read. I have reordered my accounts, worked well.