(DeepL is awesome :) )

> but why can't it be used with Firefox Sync active?

This reason is nothing that can easily be worked around, I'm afraid: Firefox sync changes bookmark IDs when it syncs bookmarks. Floccus needs those to be persistent, however, to detect the correct changes in the bookmarks tree. I know that this is not ideal. If you are willing to give up some features of Firefox Sync, however, there are other extensions that work quite well with self-hosted servers like nextcloud as well to sync e.g. passswords.

In any case: Thanks for you feedback!

Cheers