A RouterOS v7.8-compatible script for automatic generation of an address list containing all Facebook CDN addresses required for maintaining a normal connection from the DNS cache entries. Designed for decent stability and low CPU usage spikes. This is a combination of scripts by @jgrossiord and @ZloyXEP with some additions.

facebook-cdn-vpn

:delay delay-time=#REPLACE_THIS_WITH_SOME_ARBITRARY_RESULT_OF_HITTING_YOUR_NUMPAD_WITH_A_FIST#ms;
:foreach i in=[/ip dns cache find] do={
# Turn this on while turning off other delays for ease of manual use. Don't forget to reenable later.
#	:delay delay-time=5ms;
	:delay delay-time=50ms;
	:local cacheName [/ip dns cache all get $i name];
	:local cacheType [/ip dns cache all get $i type];
	:if (($cacheType="A" or $cacheType="CNAME") and (($cacheName~"^([0-9A-Za-z\\-]*\\.)*facebook(\\.[0-9A-Za-z\\-]*)*\\.?\$") or ($cacheName~"^([0-9A-Za-z\\-]*\\.)*fbcdn(\\.[0-9A-Za-z\\-]*)*\\.?\$") or ($cacheName~"^([0-9A-Za-z\\-]*\\.)*fbstatic(\\.[0-9A-Za-z\\-]*)*\\.?\$") or ($cacheName~"^([0-9A-Za-z\\-]*\\.)*fbexternal(\\.[0-9A-Za-z\\-]*)*\\.?\$"))) do={
		# IP-based rule
		:if ($cacheType="A") do={
			:local cacheData [/ip dns cache all get $i data];
			:local record [/ip firewall address-list find where (address=$cacheData) and (list=vpn_loopback_sites_dynamic)];
			# One day I just randomly found 0.0.0.0 in the list. I'm not sure how it got there, so I introduced this safety measure.
			:if (($cacheData~"^0\\.") or ($cacheData~"^10\\.") or ($cacheData~"^127\\.") or ($cacheData~"^192\\.168\\.")) do={
				:put ("script tried putting $cacheData into the address list, was prevented");
			} else={
				:if ($record="") do={
					:put ("add: $cacheName $cacheType $cacheData");
					/ip firewall address-list add address=$cacheData comment=$cacheName timeout=14d list=vpn_loopback_sites_dynamic
				} else={
					:put ("renew: $cacheName $cacheType $cacheData");
					/ip firewall address-list set $record timeout=14d;
				}
			}
		}

		# Domain-based rule
		:if ($cacheType="A") do={
			:local record [/ip firewall address-list find where (address=$cacheName) and (list=vpn_loopback_sites_dynamic)];
			:if ($record="") do={
				:put ("add: $cacheName $cacheType");
				/ip firewall address-list add address=$cacheName timeout=14d list=vpn_loopback_sites_dynamic
			} else={
				:put ("renew: $cacheName $cacheType");
				/ip firewall address-list set $record timeout=14d;
			}
		}
		:if ($cacheType="CNAME") do={
			:local cacheData [/ip dns cache all get $i data];
			:local record [/ip firewall address-list find where (address=$cacheData) and (list=vpn_loopback_sites_dynamic)];
			:if ($record="") do={
				:put ("add: $cacheName $cacheType $cacheData");
				/ip firewall address-list add address=$cacheData comment=$cacheName timeout=14d list=vpn_loopback_sites_dynamic
			} else={
				:put ("renew: $cacheName $cacheType $cacheData");
				/ip firewall address-list set $record timeout=14d;
			}
			:local record [/ip firewall address-list find where (address=$cacheName) and (list=vpn_loopback_sites_dynamic)];
			:if ($record="") do={
				:put ("add: $cacheName $cacheType");
				/ip firewall address-list add address=$cacheName timeout=14d list=vpn_loopback_sites_dynamic
			} else={
				:put ("renew: $cacheName $cacheType");
				/ip firewall address-list set $record timeout=14d;
			}
		}
	}
}