how can I apply parental control on adult sites

Install this filter: http://www1.k9webprotection.com/

Here's another one: https://addons.mozilla.org/en-US/firefox/addon/foxfilter/

Thank you for your ideas. I was planning to get an internet filter soon and this one looks good.

You're welcome.

Could you please click the "Solved It" button next to the post which solved the problem for you? This will help others searching for a solution to the same question.

Thanks.