Blocking websites for a user account I want to block certain websites for a user account - but at the same time still allow all the other accounts on the computer to access the sites - whats the best way to do this ? 

I was looking at Firefox add on but these are pretty easy to get around - ie. just change the browser, is there a user account wide way to do this ?
It sounds like you need the Parental Controls preference pane in System Preferences. About six seconds into this video there's a screenshot suggesting you can limit access to certain websites: http://support.apple.com/kb/VI28