[chaley]

Originally Posted by kiwidude

Is that not the same effect as just turning on highlighting that you can do now? I just tried it, the green highlights select the different rows. The problem is that without the custom column I have no way of sorting the results to appear together...

Not quite. The scenario was:
1) show books in all groups
2) have next-group highlight the books in a group.
This lets me see the global view, shows me what is in a group, lets me cycle between groups without the screen repainting, and also lets me find (at some level) books that are in more than one group (it gets highlighted more than once). I do recognize that this mode is not particularly useful if one has more than a screenful of duplicates.

Already exists. Add the plugin to your toolbar now. When you click on the button the first time, it detects you have no duplicate groups so pops up with the Find Duplicates dialog. Once you have duplicate groups, clicking it again is the same as next group (and ctrl+click on it for the previous group, though perhaps that may be more useful to have as "Show all duplicate books").

Ahhh...

I put the plugin on the menu bar instead of the tool bar to save real estate. The menu bar doesn't have default-click/pull-down behavior. When I put it on the toolbar, it behaves as you describe. Not sure I would have found it, though.