How can I make "oldest message first" the default setting for threads on yahoo message boards.?

On my work computer and on my smartphone, when I look at a thread on a yahoo message board, it shows the oldest message first. However, on my home computer, suddenly one day it started listing the newest first, and it has stayed that way. I know how to change it for an individual thread, but how can I change it globally - so that the default for all threads is to have the oldest message first?