Saves you from ever having to see another post about certain things ever again (idea by bjornstar, rewritten by Vindicar).
First, this script has not been maintained for years. It's entirely likely that it doesn't even work anymore. You could look for other scripts based on it.
Second, check Greasemonkey button on the browser toolbar. It should open a menu with an entry for each script you have installed, so check the entry for this script.
How do I use this script? I don't see any kind of button or link on the tumblr website that allows me to configure settings. What am I missing? Please help, thanks.