Developer reply by DW-dev
Rated 4 out of 5 stars
Slows down the deletion of mails & RSS feeds dremendously (when pressing the DEL-key repeatedly - lets say 20 times - in order to delete 20 rss feeds from the thread pane).
After deactivating the Add-On, everything works normal/fast again.
This problem is fixed in Version 3.3 which works with Thunderbird 3.1.
To create your own collections, you must have a Mozilla Add-ons account.