Review for QuickFolders (Tabbed Folders) by mark barnes
Rated 5 out of 5 stars
Awesome!
I have lots and lots of folders and sub-folders. There are a few that get many emails from my filters. This extension makes it easy to know when these folders have new email (open these folders without having to keep navigating all the way down to open them.
To create your own collections, you must have a Mozilla Add-ons account.