You must have removed everything from FSDT without ever replying Yes to the "Do you want to remove the Addon Manager" question so now, you don't have anything left to remove, meaning you lost the chance to reply to the question.
It's enough to install ONE FSDT product, then uninstall it, and this time, don't forget to reply Yes to the above question so, finally, on the next install, the folder selection will be available.