Review for Owl for Exchange by Armin W. Sauer
Rated 5 out of 5 stars
I am using the EWS-variant and it is working extremly stable. Apparently it also works now for address books and calendar - task not, but this is from my point of view not such a big one anymore, as those are nowadays quite often managed outside of Exchange. The developer was very responsive for issues in earlier versions and effectively fixed them.
This review is for a previous version of the add-on (0.7.6).To create your own collections, you must have a Mozilla Add-ons account.