Rated 4 out of 5 stars

I know about that. Right click Folder and click duplicate messages...; A window appeared and showed me all duplicate things, I followed the instruction, and click on duplicate list (left click) for message to display, but nothing happened ?? I use thunderbird 3.1.15

Léirmheas ar leagan níos sine den bhreiseán seo (0.1.10).  Rinne an t-úsáideoir seo léirmheasanna eile ar an mbreiseán seo.

Did you click or double click the messages? Actually the state of an E-Mail should toggle between "KEEP" to "DEL" when you double click them.