Amazon Discount Filter Search

Amazon may have broken it. Doesn't seem to do anything. I tried it with "Prime only" on, and off, didn't make a difference, it doesn't work. Perhaps the mechanism it uses was discontinued by amazon. (this extension adds: &pct-off=?-?) to the end of the amazon search results page's URL. ? and ? stand for the lowest allowed discount percentage, and the highest, respectively. I tried doing that manually and got the same result. I suspect this is amazon's fault.