First: works as it should without any restriction, very very good extension both for Firefox and my Nextcloud. Fifth star not assigned in fact that there's no Firefox add-on for Android version and so it is not usable for me for I don't have other devices to sync than my Android ones.
A minor proposal: A list view of the bookmarks like in Firefox itself would increase usability. The graphics for each bookmark are a bit large and if you have hundreds like me or maybe a thousand of them you're forced to scroll a lot or to use the search bar extensively.

Appendix: The list view is a comfortable advantage, thanks a lot.