Rated 2 out of 5 stars
When Mozilla integrated this add-on in Thunderbird, they removed the ability to set things so that a folder's unread count is limited to that folder only, and not all of its subfolders. Fortunately, you can change this behavior in the preference editor. Simply change "mail.folderpane.sumSubfolders" to false, restart TB, and all will be well again.
That is, until they rip out that option, too.