Review for Extra Folder Columns by joern
Rated 1 out of 5 stars
It's nice, this try to give us the extra-columns back.
But first, it is an add-on only, I miss this feature as built-in feature, and I'm not able to understand why this feature has been tossed away by the Thunderbird developers.
Secondly, this add-on doeas not bring back the main function of this feature: to show the summary for closed folders. You always have to open all folders of a tree to know how much mail are stored there.
To create your own collections, you must have a Mozilla Add-ons account.