The two location of the prefixes list is in the forum view page and in the node list.
As you can see in the image below there are two prefixes in the forum: "Book Reviews" and "Game Reviews", once you click in each one of the prefixes will redirect to the forum only showing the threads with that prefix:
This is the forum view page, the prefixes are all listed in the forum description, as you can see again the same forum, with the two prefixes "Book Reviews" and "Game Reviews":
There is no option to show the numbers of thread of each prefix because the version of this addon is a request from an user.
You may not redistribute this or any of my other add-ons without permission.