Hi, am perfectly willing to change my rating - but as of right now = I get zero results. I had it run one week ago for a full day. It simply showed "0" on everything.
I have 124792 bookmarks [well, am online since 1993 :)]
So, it is virtually impossible that there is none broken, or double etc. I know for a fact that I have at least over 20 thousand doubles, because of a inadvertent new import after Xmars closed.
That was my reason for installing your extension, hoping to clean first before I use bookmarks also with my FVD account I have for speed dials.

Yes, of course I can do a manual check and clean with the library, but this would be silly if a extension like yours exist.
I have:
Firefox quantum 60.0.2
Your extension version: 2.0.1
I read over every comment here without being able to determine anything to solve my problem.
Hoping you will respond to the low star mark - and maybe there is an explanation for zero results.

I also tried it on my laptop, that is not synced to anything. The only identical setup is the old Xmarks bookmark folder structure.
I always kept the Xmarks clean on all my cpu's [had used them from their initiation date].
I should be able to get at least some number of duplicates from your extension.
Tests I did following last weeks zero result after an entire day run: Tried also with a new mozilla profile,
but still get no results.
I see that others here have no problem, so I need to find out what and why I get no results.
Kind regards,
Michele
Ps: ich spreche auch Deutsch, sollte das fuer sie einfacher sein.