Lior Levin asked me today if it’s possible to create a Firefox extension, that will block Facebook part of the time. As a result, I created a Firefox extension (a compiled Greasemonkey) that blocks Facebook for 45 minutes each hour (form :16 to :59), i.e. blocking Facebook for 75% of your time.
This is a very rough alpha version. It will work, but it has a lot more to do with.
Will be glad to hear if you’re using it, and what you think of it.