If you are an active ShutterStock (www.shutterstock.com) user, then like most people you may have created 'Lightboxes' (ShutterStock's version of User Collections). However, every time you go back to your Lightbox, Shutterstock gives you no way of knowing which of the items/images on the page, you have already downloaded. This script reads from your Download history and visually marks any items on the page, that it finds you have already downloaded. This way you can save time and work only on the yet to be downloaded images. This addresses a very common complaint for most ShutterStock users.
Install Greasemonkey to Firefox or Chrome (http://userscripts.org/about/installing). Go to http://userscripts.org/scripts/show/164316 and install.