Your comments

28/11/19 I have read the article above and tested multiple scenarios. From my experience, to avoid duplicates the only way is to allow the browsers to use their own inbuilt sync option "like for like". i.e. Firefox syncs with Firefox, Chrome with Chrome, Opera with Opera and ONLY use the manual option within EverSync (uncheck auto-sync) to sync between browser types via the Eversync online repository by uploading a known "good" copy of your bookmarks ("Overwrite server data") and then download that copy to your various other browsers ("Overwrite local data"). Each browser type will then sync between themselves correctly. It's clumsy but this is the only way I have found to avoid duplicate bookmarks. Even with all inbuilt browser syncs turned off Eversync still creates duplicate after duplicate until my quota is exceeded. A neat idea but it doesn't quite work properly in my humble opinion. Free to use so I'm not complaining (much :)