Hi Andrew, thanks for trying it out, and sorry you had trouble getting it to work. I'm using it on FireFox 58 and it works for me here. Are you sure you tried it on a news article or blog post? For example, if you load this article https://www.truthdig.com/articles/empty-piety-american-press/ and click the Simple Print icon on your toolbar, you should end up here: https://pdf.fivefilters.org/simple-print/url.php?ext#https://www.truthdig.com/articles/empty-piety-american-press/

Does that not work for you?