Rated 3 out of 5 stars

This add-on adds a ridiculously long option to the right click and Tools menus so it needed removing as soon as I had used it. This may be why I removed it last time I used it.

For removing duplicates it works well.

Couple of minor annoyances which I found while I had it installed (for less than 5 minutes due to the above), telling it to search special folders gives you an error about not searching special folders, which is set in the global options. I can understand the behaviour if you were selecting the root of the account and searching everything but it shouldn't do this if you are specifically selecting a special folder only.

Once you have searched for duplicate messages and you select delete on the duplicate messages window you get a pop up confirmation. If you select cancel rather than dropping you back to the results window it just cancels the whole process and you have to start again.

This review is for a previous version of the add-on (0.3.10). 

* About the cancel-cancels-everything - you're right, it shouldn't work that way. I opened a bug and will fix it:
https://www.mozdev.org/bugs/show_bug.cgi?id=25978

* About the long right-click menu item: I'm not too happy with it myself, but - can you suggest something shorter? I don't want it to be cryptic and confusing.

* About the special folders restriction: In this case I have to respectfully disagree. You need to remember that user error with this extension can lead to Data Loss; as a result, I have to "err on the side of caution" - I remember the cases of people complaining about accidentally deleting messages from Sent / Drafts / etc.

Anyway, thanks for taking the time to write a detailed review.