Part of this app works well. With over 3000 bookmarks, this app stops checking for broken URLs at about 2400. Stops cold. The pause doesn't work at this point. There is no way to "select all" and no way to delete the bookmarks with broken URLs.
I uninstalled the app, reinstalled the app and got the same problem again. The duplicates part of the app, including the merge, works well. The broken apps? Not so much.
The search for an app goes on.

Problem solved.
All 'find' functions are fast, very fast.
Wishes:
1) A progress bar in the merge duplicate folders
2) A "Select all" option in the duplicate files result (active on ony ONE duplicate list)

Five stars even as it is.

This add on lacks instructions how to use it. Backup instructions are not enough. I tried to make this work but no success. I have at least several thousand duplicates including duplicate folders etc. It found not one duplicate bookmark.

I am a Chinese user, thanks to the extension provided by the author, from chrome to firefox..

This add-on works very well in all of its functions. The "Merge duplicate folders" feature is unique and this is the only add-on that I have found to get rid of multiple duplicate paths. It would be beneficial to have a way to see the progress during the "Merge duplicate folders" operation so that it can be seen when the operation is complete.

Fantastic tool very well done.
Just one small cosmetic suggestion, after the scan the list and addon title are not centered on screen.
See these image for better understand:
Before: http://oi64.tinypic.com/m82nep.jpg
After: http://oi67.tinypic.com/nfjpth.jpg

Great addon. Could you add an "exclude folder" option. Many session restorer addons and similar ones use the bookmarks as a backup and duplicates on those folders are very frequent and required so it would be nice to be able avoid scanning that. Thank you. Also it would be great if you could add a way to contact you like a mail or github in case someone wants to request a feature or report a bug.