Have you seen this tutorial?

http://bjornstar.com/post/44263423/how-to-setup-tumblr-savior-for

I use Firefox, and when I need to edit my blocking tags I have to click on the arrow button next to the Greasemonkey icon, then click 'manage user scripts' which then opens up my Add-ons Manager. I have to right-click on the entry for Tumblr Savior and then 'Edit.'

I think, a little while back, it stopped working for my Firefox. I had to add a 'grant' line to the code:

// ==UserScript==
// @name Tumblr Savior
// @namespace bjornstar
// @grant none
// @description Saves you from ever having to see another post about certain things ever again

I hope that's helpful!