Review for Additional Folder Views by FreeJeff
Rated 5 out of 5 stars
This add-on is simple but brilliant. I keep my Favorite Folders in the top pane, and it makes it a breeze to just drag messages from whatever the open folder is to where I want to file it. BTW, contrary to an earlier review, the Favorites Folder is in alphabetical order.
To create your own collections, you must have a Mozilla Add-ons account.