Logic is strange.

[FaltoGH]

Hello. I tested your library by using console app.

            BookmarkLink youtube = new BookmarkLink("youtube.com", "YouTube");
            BookmarkLink github = new BookmarkLink("github.com", "GitHub");
            BookmarkLink stackoverflow = new BookmarkLink("stackoverflow.com", "StackOverFlow");
            BookmarkFolder bookmarks = new BookmarkFolder
            {
                youtube, github, stackoverflow
            };
            NetscapeBookmarksWriter writer = new NetscapeBookmarksWriter(bookmarks);
            using (FileStream fs = File.OpenWrite("bookmarks.html"))
            {
                writer.Write(fs);
            }
            bookmarks.Remove(youtube);
            bookmarks.Remove(github);
            bookmarks.Remove(stackoverflow);
            Console.WriteLine(bookmarks.Count);
            using (FileStream fs = File.OpenWrite("bookmarks.html"))
            {
                writer.Write(fs);
            }
            NetscapeBookmarksReader reader = new NetscapeBookmarksReader();
            using(FileStream fs = File.OpenRead("bookmarks.html"))
            {
                bookmarks = reader.Read(fs);
            }
            Console.WriteLine(bookmarks.Count);

output:
0
2

I think second output shall be 3, if the program doesn't overwrite.
And second output shall be 0, if the program does overwrite.

Currently, I delete the file before the save bookmarks to avoid this problem.