When you say URL filtering, what are you trying to achieve?
If you simply want to block some URLs from being loaded then you could use something like
Adblock Plus. Although it's designed for blocking adverts you can supply it with any URL or regular expression. For example you could block the entire of LQ by adding "linuxquestions.org" to the filter list.
However, something like that is easily turned off by the user. So possible not so good if you want to block other users from going to certain sites.