This video tutorial belongs to the Computers & Programming category which is going to show you how to block websites in Firefox with the BlockSite add-on. Do a Google search for add-ons for Firefox and click the first link. On the home page, search for 'block websites' add-on, find it and click 'add to Firefox'. Then on the software installation page, click on 'install'. Now click on 'tools' and select 'add-ons'. Click on the 'block site' add-on and type in your password to go to the 'block site preferences page'. Here you click on the 'add' button and add the site you want to block. You can add as many sites as you want. You also have the option edit and remove sites.
Oh... and if you're working from home these days, be sure to check out Gadget Hacks' Working-From-Home Essentials.