Rated 5 out of 5 stars
This plug in reaffirms why Mozilla is better than Microsoft!!
I had created duplicate messages by accident in MS Outlook (via Exchange connection) and had 1K+ useless copies cluttering my search results.
This add-on was easy to install and with just a couple clicks I moved all my duplicates to the trash folder! (Note step 2 is to empty trash folder.)
I tried deleting messages one by one in Outlook, but after half an hour figured it is not a manual job. Luckily I had Thunderbird too! :-)
P.s. Similar plug-in for Outlook is $24! :-/ So I am so happy this is free, so I was glad to send the developer a contribution!