You can used the HOSTS file to block specific websites. <br /> http://en.wikipedia.org/wiki/Hosts_file There's the Block Site extension, too. <br /> https://addons.mozilla.org/en-US/firefox/addon/blocksite/ <br /> But it might not be updated in a timely manner for the Aurora channel ''(which you're on with 9.0a2)'' and it might be disabled after a version update in the future, although the 9.0 version is now set for compatibility.