Time Blocker

This app is a timer which utilizes the time blocking technique, in which you work/study intensively for a given amount of time, then take a short break. After a few of those, you take a big break. 

Main features:

* Three different timers for the different sessions (work/study (time block), small break and big break, all completely customizable.

* The ability to play a "ding" sound/open a small popup window when a session ends.

* Keyboard shortcuts to start any of the three given presets, or stop the currently running one.

* A badge on the icon of the add-on indicating the minutes left for the session, so you don't have to open the add-on to know the time left.

* The ability to continue from the Time Block session to the Small Break session.

Source: github.com/igorkheifetz/timeblocker