Software or addons for blocking websites

Can anyone recommend a free software or an addon(for home user) that block websites based on keywords, e.g. keyword: games, the software or addon must block all websites which contain the word 'games' in the urls, in firefox and internet explorer.

Thanks

 

Not sure these will help or not. Check them out and see-
http://www.opendns.com/solutions/overview/
http://www1.k9webprotection.com/index.php

 

K9webprotection seems to do the job.
Thank you