Review for Folderpane Tools by Andrew P.
Rated 4 out of 5 stars
Works with SeaMonkey 2.8 mail client, although the messages it displays are Thunderbird-specific and the installer is getting rather dated. I had to unzip the XPI archive and modify the install.rdf file with a text editor to allow installation in this version of SeaMonkey, changing the maxVersion value from 2.5a1 to 2.8, then re-zip it into a new archive and change its extension to .xpi. Fortunately, this is something that even a novice user should be able to do. (This review pertains to Folderpane Tools 0.6.1.)
To create your own collections, you must have a Mozilla Add-ons account.