Rated 4 out of 5 stars
News version 1.0.1 (author's website) works on FF 3.5.2.
+ A must-have add-on for anyone with a huge bookmarks number !
+ Real-time duplication feature's great, e.g. when concatenating different bookmarks files.
Would be great to add following feature : Comparing 2 folders recursively and either 1) deleting every duplicated bookmarks in one of those folders (again recursively) or 2) move every not-duplicated bookmarks from one folder to the other.