I wrote another script at Greasyfork. Here’s my profile.
This one adds a “filter” feature to the ebay selling list so you can quickly find specific items.
Greasyfork is a repository of scripts for Greasemoney and Tampermoney, web browser extensions that allow you to execute your own Javscript code on any web page.
This means you can create elements, insert them onto the page, and do automate some repetitive tasks.