This method will not effect any other website, i would like to block Facebook in my example.
1: Add website in Layer7 Protocol.
/ip firewall layer7-protocol add name=facebook regexp="^.+(facebook.com).*\$"
2: Add your DNS, ISP and your DSL modem IPs and gateway in firewall address list for exception.
/ip firewall address-list add address=188.8.131.52 list=not_this_dst add address=184.108.40.206 list=not_this_dst add address=10.0.0.1 list=not_this_dst
3: Create mangle rule for filter facebook IPs
/ip firewall mangle add chain=forward action=add-dst-to-address-list protocol=tcp src-address=192.168.88.0/24 dst-address-list=!not_this_dst address-list=facebook address-list-timeout=0s layer7-protocol=facebook
Now you get all facebook IPs from firewall connections in firewall address list like this,
4: Now create another mangle rule for facebook connection from filtered IPs list.
/ip firewall mangle add chain=forward action=mark-connection new-connection-mark=facebook passthrough=yes dst-address-list=facebook
5: Now block this facebook connection from firewall filter
/ip firewall filter add chain=forward action=drop src-address=192.168.88.0/24 connection-mark=facebook
If you want to allow facebook to some or one user you can add exception IPs in rule, for this add those IPs in firewall address list
/ip firewall address-list add address=192.168.88.101 list=not_this_src add address=192.168.88.120 list=not_this_scr add address=192.168.88.155 list=not_this_src
Remove previous firewall filter rule and add new like this
/ip firewall filter add chain=forward action=drop src-address=192.168.88.0/24 src-address-list=!not_this_src connection-mark=facebook
Or you can edit and add IPs in your previous rule.
Are we done? NO.
Someone bypass your mikrotik firewall using VPN tool, in this condition you can use OpenDNS for block proxy or VPN tools.
Note: This method will not works just for youtube, you can block youtube videos from L7
/ip firewall layer7-protocol add name=videos regexp=videoplayback|video
Sorry, i made some mistake in my method, now i edit it.