v159 not showing unread mail tray icon (bug2087747)

I always keep program icon in tray and when a new/unread email arrives, a separate yellow icon would pop up next to it... Well, after updating from 158 to 159, that new/unread icon is no longer popping up. Now I have to periodically click the main program icon to open Thunderbird and see that there's tons of new/unread mail sitting there, but that yellow tray icon never showed!

I would like to roll back to 158 but it is proving to be quite difficult.