It's not a matter of add-on options. For me it works with thousands of bookmarks like a charm. Of course add-ons like this (and any othe broken bookmarks checker!) work better with a stable internet connection. If your internet connection is not able to handle many requests at the same time it will lead to more false negatives. That's the nature of such add-ons. As such it's seems a bit a unfair rating to give only one star.