I like the simplicity of this add-on. It just consists of 5 buttons - a button for 25-minute Pomodoro chunks, 3 buttons for 5-, 10-, and 15-minute breaks, and a button for resetting the timer. While the timer is running, it also displays the remaining minutes on a small number on the toolbar icon, which is pretty convenient.

Unfortunately, it's so simple that some basics are missing.
- No alarm sound when timer is finished
- Break timer doesn't automatically start
- Doesn't really support the long break after 4 Pomodoros

Would use it again if the above features are added.