What methods exist to de-duplicate Firefox bookmarks.

As I search Google I find that there previously was a plugin called CheckPlaces, but that no longer seems to exist. Another popular suggestion seems to be AM-DeadLink, which I tried, but it completely trashed my bookmarks. (Fortunately I had a backup first, and yes I had closed Firefox first as instructed).

I was trying to move all my youtube.com bookmarks into a folder. I tried doing a search, and then dragging the bookmarks into the folder. Apparently this creates a copy, instead of moving them as I expected. So now I have 3 of everything since I had tried a couple times.