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CloseReview for Extra Folder Columns by unknownhtml
Rated 5 out of 5 stars
I have used this since it was first published and will miss it but this functionality is now built into v38.x.
Go to View - layout - Folder Pane Columns and select -
Exactly like this add-on now just built back in...finally!!!
You will need to enable the MENU bar to see VIEW and select from there if you are using windows. I haven't checked out Mac options yet but will test on VM and report back later.
You do NOT need to enter any config editor option to enable.
To create your own collections, you must have a Mozilla Add-ons account.