The latest update broke the popular script and this is a replacement for it.
First install the script, then go to http://www.tf2outpost.com/trades. Right-click the page and under Reload Every choose 15 minutes. Firefox will then refresh the page every 15 minutes. When a trade shows up that isn’t bumped, the script will bump it.
(You might need a reload extension for Firefox. I recommend https://addons.mozilla.org/en-US/firefox/addon/reload-plus/)