While you can use Web Filter's Categories feature to block whole types or groups of websites, you also have the option to block individual websites via the Block Sites list.
Blocking a website
Go to Apps > Web Filter > Block Sites. Enter the domain only, surrounded by asterisks: a sample entry for YouTube would be
Note that some sites use multiple URLs, so you may need to enter others to block all possible ways to reach the site. It's usually not necessary to block link-shortening services because those simply redirect to the main site URL. For example, fb.me is a redirect to facebook.com, so a single Block Site entry for *facebook.com* would be effective.
Disabling the block page
NGFW's default behavior is to inject a block page into the connection that alerts the user that the site they are trying to reach is blocked. If your environment is not using SSL Inspector and does not have the NGFW's root certificate authority installed to client devices, you may receive a security warning error message in the browser when an HTTPS page is blocked.
You can disable the injection of the block page in Web Filter > Advanced by enabling the option "Close connection for blocked HTTPS sessions without redirecting to block page". This will cause the page to be blocked "silently", without any notice to the user (and without generating the warning in the browser).
Using a custom block page
You can also redirect the browser session to a customized block page you have built yourself and hosted locally. Go to Web Filter > Advanced and enable the "Custom Block Page" option, then specify the location of your custom page.
Using wildcards for best results
We also recommend using wildcards whenever possible, to make your Web Filter rule entries as effective as possible. Please refer to this article for more details: Improving filters with wildcards!Follow