When reading the newsgroups I follow in Thunderbird, I always like the most recent messages to be displayed on top. However Thunderbird adds them on the bottom by default. No problem there, however when resorting the column, it unthreads the messages, so you need to group them together again. Why? because a setting in thunderbird tells it to. So, in the Options on the General tab, select the config editor and change the the value of mailnews.thread_pane_column_unthreads to false. Now, when resorting the messages by hitting the column title, it keeps all of them grouped by thread.