https://support.mozilla.org/en-US/questions/1326829

Toggle mail.delete_matches_sort_order to true: If you set View -> Sort by -> Descending when you delete a message it will move the selection up to the next most recent message (rather than to the next oldest message).

Settings/General/Indexing/Config. editor

Actually, I tried it and still have the same problem--it moves the cursor to the message below the deleted one (i.e., to the older message). I should say that I have the messages set with the most recent at the top rather than the bottom. I tried both Descending and Ascending and get the same results (same as before)--except that when I select Descending, the order is reversed with oldest messages on top and newest at the bottom. I want to keep the newest at the top but be able to delete upward fro the bottom (older to newer). Possible? Thanks.

I have the Threads Pane set to Descending, so newer messages are at the top. When the preference is true, after deleting a message the message 'above', or newer, is selected. So I can't explain why it doesn't work for you.

I'm a new user of Thunderbird, so I'm fairly ignorant. I don't know to "Toggle mail.delete_matches_sort_order to true," but I did have View -> Sort by -> Descending in the menu, so I did that. How and where do I do the former?

Threads on my menu doesn't have Descending (or Ascending) as an option.

Thanks a lot for your help.

Config. editor is at the bottom of Settings/General/Indexing. In the Advanced Preferences tab, type matches in the search box and click the Toggle icon to make the relevant pref. true (see picture).

That did it. Thanks so much. I'd have never found or known that. Happy Thanksgiving (if you're in the U.S.== otherwise happy Thursday)