That sounds awful. Can you export your bookmarks as csv or json? If so, you can use duckdb (or xsv) to clean any duplicates.

While you're at it, I'd recommend to consider uploading the new bookmarks to a dedicated bookmark manager and avoid having the browser manage your bookmarks. For folks who rely on bookmarks, dedicated bookmark managers offer great value (eg. auto-archiving a copy of every bookmark to combat link rot). I currently use Raindrop, but if I were to start fresh I'd go with Linkwarden instead.