After pretty much giving up on getting POP to work for Thunderbird (there is an add-on called ypops but I could not get it to work), I just
came across a brilliant workaround! Go to account settings (I had to go to the index of Yahoo services to find it) and switch to Yahoo in Asia (I did Philipines) you don't have to switch your time zone, so no worry about time stamps.
No need to pay 20 dollars a year for Yahoo Plus!