Unfortunately, it doesn’t work; the extension finds 220 duplicate bookmarks but doesn’t display them, so it’s impossible to check them before deleting them. The only page that appears has five empty fields labelled ‘180x’ and ‘Data:’, along with two buttons at the bottom – ‘Clean Bookmark’ and ‘Scan Again’ – and that’s it.
It’s a shame for a tool that seemed simple and quick...

Compared to the others, this one is much cleaner & easier to use, plus it can remove broken bookmarks as well.