This is by far the best bookmark manager. It finds duplicates with a single click, then offers options to select them (another click can select all duplicated bookmarks, except the first, and one more can remove the rest, couldn't be any simpler!) What's best about this extension is not even the options: while others do whatever they were supposed to do silently, keeping one wondering if they're working or just failing and crashing quietly, this one shows a nice progress bar! It also has an advanced filter mode that can go beyond exact duplicate finding.