Rated 5 out of 5 stars

Works as adverstised. Finally, My Archive Folder can be marked as read :)

Rated 2 out of 5 stars

A very useful addon, but I have 4 email accounts. When I right-click on the first one and select 'Mark subfolders read' it marks every message in every email account read. Not what I was expecting !!

This review is for a previous version of the add-on (1.0). 

Thank you for the information. I did not consider using this on an account instead of a folder, and there seems to be no way to limit the menu entry to the latter.
So, I put something in to handle accounts specifically (finally). This should be fixed in version 1.2 (which is currently pending review).