Hi,
As far as i know, this is not possible.
If you have enabled url filtering and have redirected the traffic to a url filtering server, then probably you will get the logs
from those systems.
Otherwise if you have a proxy server/WCCP servers in your network, you can get the URLs accessed details from them.
From firewall, you will only get layer3/4 information in the syslog, not the URLs accessed.
-VJ