Review for Contacts Sidebar by David Burleigh
Rated 4 out of 5 stars
Great addition, that I really miss in 3.0. I hope the new version will have an option to require confirmation of deletions from the contacts list. It is so easy to just hit the delete key by accident and lose a contact when the focus is on the Contacts Sidebar.
To create your own collections, you must have a Mozilla Add-ons account.