Content filtering on Ubuntu 10.04

You might take a look at http://www.opendns.com/

They have free DNS service (as well as paid upgrade services). By setting up a free account and configuring your machine(s) or to use their servers, you can set categories that you want blocked and they wont allow access to those sites. Below is a list of the categories available for blocking in the basic free service. Their servers also respond significantly faster than my ISP's DNS servers.

Academic Fraud, Adult Themes, Adware, Alcohol, Auctions, Automotive, Blogs, Business Services, Chat, Classifieds, Dating, Drugs, Ecommerce/Shopping, Educational Institutions, File storage, Financial institutions, Forums/Message boards, Gambling, Games, Government, Hate/Discrimination, Health, Humor, Instant messaging, Jobs/Employment, Lingerie/Bikini, Movies, Music, News/Media, Non-profits, Nudity, P2P/File sharing, Parked Domains, Photo sharing, Podcasts, Politics, Pornography, Portals, Proxy/Anonymizer, Radio, Religious, Research/Reference, Search engines, Sexuality, Social networking, Software/Technology, Sports, Tasteless, Television, Tobacco, Travel, Video sharing, Visual search engines, Weapons, Webmail

I believe what you are looking for is in this thread.

http://ubuntuforums.org/showthread.php?t=843510

No problem! You'll find this is the case with a lot of software for internet purposes: it's not installed separately, it's a plugin. This applies especially for proxies.