Such a pain for nothing and very sad to write a bad review. I'm using Nextcloud 19 and Nextcloud Bookmark 3.4.9 with floccus 4.5.0. The first sync process load very heavy the memory of my firefox 78.8.0 ESR (more than 3Gigabytes with one empty tab open !) and of course Firefox is lagging/unusable during the syncing process. After one hour the sync is done, but not usable to another computer. On the other computer with Firefox, I can see only empty bookmark folders. I tried to read the user guide and FAQ but nothing clear. I start to think this add-on is not made to sync bookmarks accross other Firefox, it loads too much Firefox and sync is too slow (my Nextcloud serveur work flawlessly).