Select folder View > Sort by > Threaded View > Threads > Expand all threads

To force this on other folders either click on the 'select columns to display' icon or right click on the column headers bar at bottom select 'Apply columns to' select 'Folder and it's children' select account name > select account name. Or select specifc folders if that is required.

However, this also sets all the columns as well, so you may need to alter eg: 'Sent' and 'Drafts' as the 'From' column header may not be required and perhaps 'Recipient' would be required.

Changing the sort or collapsing threads and then exiting Thunderbird will get stored in the session files and when you next open Thunderbird, it will open using last session data.

Hello Toad-Hall. Thanks for the reply. However, the simple setting in "View" does not work beyond "occasionally" within a give session. To be clear: View > Sort by > Threaded View > Threads > Expand all threads... 1. Will not continue to keep that sort and expand threads inconsistently throughout a session. 2. Will never start the same in a following session. Often, the "sort by threads" will survive a new session. "Expand all thread" never does. I have to "re-set" often within a session. And always in a new session. Thanks again. /s