Yes, there will be duplicates in the newly imported folders; they won't be sorted into the existing folders. Over the years users have created extensions to "de-duplicate" your bookmarks, but I don't know which ones are still working. Also, please make an extra backup before using any of them, "just in case." * [[Restore bookmarks from backup or move them to another computer]] * Some candidates to consider: ** [https://addons.mozilla.org/firefox/addon/bookmark-deduplicator/?src=search Bookmark Deduplicator] ** [https://addons.mozilla.org/firefox/addon/bookmarks-organizer/?src=search Bookmarks Organizer] - after you click its toolbar button, make sure to change the function to Duplicates before clicking the Check bookmarks button, otherwise it tries to connect to all the sites in your bookmarks to validate the links - ''in my test, this was time-consuming to use because it shows you a list of all the matches across all folders rather than telling you, for example, all of folder X already exists and letting you remove folder X with a single click''

In case you do not need to keep all IE favorites you previously imported and they are still in one folder then you can remove this folder and only keep the newly created folder with the IE favorites.