Here's a link to the washers we are talking about
:
http://www.clotilde.com/detail.html?prod_id=6966
They are thin pieces of Teflon that are shaped just like washers (the little discs that go between wood and a screw's head to protect the wood from the screw). You place a washer inside your bobbin case before inserting the bobbin. They cut down on static and prevent the bobbin from "whipping" the thread around, something that can cause a bird's nest.
Here's an additional link with more information:
http://www.daystyledesigns.com/magicgeniewashers.htm