Review for Quicker Filer by Metallian
Rated 5 out of 5 stars
This tool is probably the one I use most because I have a folder tree with more than 400 folders.
The only missing feature is the possibility to copy a whole folder in another folder (including all messages and subfolders) the same way as copying a message in a folder.
To create your own collections, you must have a Mozilla Add-ons account.