Review for Extra Folder Columns by Larry Gusaas
Rated 1 out of 5 stars
I just tried version 0.4. It breaks smart folders.
My Smart Folders inbox, when expanded contains inboxes fro each of my accounts. Each was listed with the name of the account. With 'Extra Folder Columns' enabled the name of each account is missing. This makes the extension useless. for me. It takes away way more than it adds.
To create your own collections, you must have a Mozilla Add-ons account.