User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:18.104.22.168) Gecko/20080404 Firefox/22.214.171.124 Build Identifier: version 126.96.36.199 (20071031) In threaded view selecting a rolled up thread and then pressing delete should delete (move to trash) the entire thread. not just the message at the top of the thread. GMail works this way, and it's very helpful in managing large volumes of uninteresting threads. Reproducible: Always Steps to Reproduce: 1. 2. 3.
A related note: if I select both the thread and one other message outside the thread (with shift click) then press delete, the entire thread is deleted, along with the additional message. Only deleting the first message when I only select the thread is inconsistent.
That threaded view issue bug is good for one thing... it makes finding simple dupes like these easy :-)