I recently started using this after my previous one started acting up. I really like how the volume of the notification sound can be adjusted, and that the sound can even be changed (though I have not tried it myself since I am fine with the default one). A possible improvement that I would look forward to is to allow setting the break time in seconds. I use this extension (as well as my previous one) in short intervals and short break times. Currently, it seems like the minimum accepted break time is 1 minute. Trying a value like 0.5 to get 30 seconds prevents the settings to be saved. Thanks for this extension!