see http://kb.mozillazine.org/Blocking_bad_sites_and_annoyances For links see following topic links in the article -- MozillaZine doesn't like to link to things twice See also -- More information: on extensions and items mentioned in this article I would suggest Blocksite if you want to specifically block some sites, I use several things, basically most of the things in the article except parental controls and kiosk type operations. The link for Blocksite (16.4 Kb) -- https://addons.mozilla.org/firefox/addon/blocksite/ If you already have "Adblock Plus" you can use it

To block a website on the entire PC - for '''''all browsers''''', you can use the HOSTS file. <br /> http://en.wikipedia.org/wiki/Hosts_file