Copyright © 2009 Mayank Lahiri
Released under the terms of the GPL.
What is it?
A small script that enhances Google Scholar by letting you cross-reference Scholar's "Cited by..." lists. For Firefox only.
Why?
Choose a set of papers, even across searches, and find all references that cite every paper in the set. Useful for narrowing the scope of citations you're looking for.
In pictures:
1. Select documents from any Google Scholar result page, even across searches:

2. Click the "citation explorer" link to start retrieving citation lists from the server. This might take a while, and only the first 1000 citations for each document you select are retrieved. This is to be nice to Google's servers, and so that your computer doesn't get temporarily banned from Google.

3. The results interactively show common citations for the documents you select.

Installation
  1. In Firefox, install the Greasemonkey add-on if you don't already have it (one-click installation). Alternatively, in the browser window, go to Tools -> Add-ons -> Get add-ons and search for "Greasemonkey".

  2. With Greasemonkey installed, click this link to install the Google Scholar Citation Explorer script. In Firefox, click "Install" in the window that pops up. Alternatively, if you'd rather check out the source and reviews first, visit the UserScripts page.

  3. Visit Google Scholar and use it as you normally would.
Feedback, suggestions, etc.
Use this page, or mlahiri at fb dot com.
Disclaimer
This script is not related in any way to Google Inc. It's something that helped me through my own Ph.D. research, and which I hope will be useful to other people, purely for academic use. There are no ads involved, and I benefit in no way from your use of this script. Now stop procrastinating about how to do research better and actually go do some research.