It would be better if user can set timer for websites and if time gets over then it alerts him. For ex: I can get 30 minutes for YouTube, once 30 minutes gets over this extension should give an alert. Moreover, Browser timing can be set. For ex: When i take break from study i browse, it would be good if i can set timing for 20 minute on my browser and after that it alerts me.
Later I explored this add-on, the second feature is there. Still including first feature would be worth it.