This is a Firefox extension. Open wintermelon.xpi in order to install the addon. This addon is compiled with JetPack.
You can read about what this addon does on my blog. It is basically an implementation of XKCD #862, which places a time delay whenever I try to access Facebook, Gmail, Art of Problem Solving, etc.
One can adjust the websites and timeouts by modifying the preferences from the Add-Ons menu. The options should be fairly self-explanatory :)