Hi Anoop,
SGOS provides you option to choose a User-Agent from the pre-defined list or you can create your own by using respective identification strings. You can use the source object of "Request Header…" to create this. Select the header name as User-Agent and fill the Header Regex with the string required. Example below is for Firefox 34.0 in all OS platforms. You can then use this to deny.
String to use for FF 34.0:
^Mozilla.*Firefox/34\.0$
CPL equaling for blocking this FF user agent is below
<Proxy>
request.header.User-Agent="^Mozilla.*Firefox/34\.0$" Deny
Note: User-Agent strings can be easily manipulated by used third-party plugins in browsers