After I switched from Chrome to Firefox, the first thing I was looking for was an alternative to StayFocused add-on, and a little Googling led me to this incredibly useful add-on for Firefox. What follows is my first impression, not a fuller review:

1. It is relatively easy to access the settings here. It should not be because when I am addicted to a site, I would just simply change the setting after my allocated time expires. Thus, the very purpose of using the add-on becomes pointless. It should be much more challenging to change the settings so that we are "forced" to maintain a strict schedule. I would request the developer to put this on their priority list.