Rated 5 out of 5 stars

Wonderful! This works beautifully with large IMAP folders (>1k messages).

I have just two complaints:

1. Needs an override option to search special folders like Sent.

2. It would be nice if it automatically preferred duplicates that have been replied or forwarded (the green and purple arrows).

This review is for a previous version of the add-on (0.3.2). 

1. In the extension's options window, uncheck 'Skip Special Folders'.

2. Make the message flags field visible, sort by it (click the appropriate column once or twice for the reverse order), then select 'Keep First'. This does the job in most cases, as the HAS_RE(ply) is copy is kept, or removed, depending on the sort order.