Step 1: Install the Firefox web browser (if you haven’t already done so).
Step 2: Install the LeechBlock extension from the Mozilla Add-ons site. Note that you will be asked to restart Firefox to complete the installation.
Step 3: Select LeechBlock > Options… from Firefox’s Tools menu (or the right-click context menu) to specify which sites to block and when.
Step 4: (Optional) Add the LeechBlock button and/or countdown timer to one of Firefox’s toolbars (right-click on the toolbar and select Customize…).
That’s it! You’re good to go.