Review for compactfolder by thuldai
Rated 5 out of 5 stars
Very useful, particularly the shortcut key (Shift-E) that is added for compacting a folder.
That's how I use this Add-On mostly: sort through emails, mark some as deleted; review quickly to make sure, then hit Shift-E to have them gone.
Severely recommended!
To create your own collections, you must have a Mozilla Add-ons account.