how to block the below site using web filter

The site itself appears to employ some some sort of browser hijacking, according to google.  If your fgt are not using SSL "Deep-inspection" then certificate-inspection should be used - this causes the fgt to look at the domain name listed on the web site's security certificate - in this case the common name appears to be "downloadmyinboxhelper.com", but other names listed on the security certificate are *.downloadmyinboxhelper.com and *.hdownloadmyinboxhelper.com.  If you want to block this site, you may have better luck using two wildcard URL filter entries; e.g. *.downloadmyinboxhelper.com and *.hdownloadmyinboxhelper.com.   Personally, I would see about "disinfecting" the machines that have this site loaded in the browser as a a "search engine".