Raindrop prevent saving duplicates when you use our browser/share extensions, always.
But even if this indicator is not enabled, Raindrop extension WILL prevent saving duplicates.
Here the list of possible cases when duplicate check can fail:
- Raindrop web app does not prevent you from creating duplicates (when you click Add in top right corner) https://app.raindrop.io/ - it's expected behaviour, just allows you to create another copy of same URL
- Browser extension can't detect saved status if URL of a page change each time you visit it. Some websites slightly change page URL each time you visit it, they add some tracking info, etc. In this case you always have different URL. Just check page URL and bookmark that you saved and check difference in URL.