This behavior is "how it's always been" in the suite as well as TB.
If you set the value of the pref
mailnews.thread_pane_column_unthreads
to False, clicking the Thread column header won't change the sort criterion; it will simply toggle between Threaded and Unthreaded. By default, this pref is True to provide the old behavior. (xref bug 219787.)
Additionally, clicking on any other column header won't change the threading, it will simply change the sort criterion or reverse the direction.
The suite additionally provides prefs UI for changing that setting.
This behavior is "how it's always been" in the suite as well as TB.
If you set the value of the pref thread_ pane_column_ unthreads
mailnews.
to False, clicking the Thread column header won't change the sort criterion; it will simply toggle between Threaded and Unthreaded. By default, this pref is True to provide the old behavior. (xref bug 219787.)
Additionally, clicking on any other column header won't change the threading, it will simply change the sort criterion or reverse the direction.
The suite additionally provides prefs UI for changing that setting.