The problem you will hit is that "a website" is not a single entity.
You can allow access to an IP address (or a number of them) quite easily, there are more modern methods than that script,
but that will not bring you much. You may know the domain name of the site itself, but internally it will load items from all
kinds of other "sites" to show pictures, advertisements, video material, to get scripts, layout information, etc.
You first need to compile a complete list of all domain names used when operating the sites you want to whitelist, and put
them in your exception list. You can do that using address lists with DNS name instead of the script:
/ip firewall address-list
add address=www.netflix.com list=allowed
add address=codex.netflext.com list=allowed
add address=assets.netflext.com list=allowed
etc etc etc until you have everything.
However, when you have that all complete, next week the sitebuilder may add another one and the site is going to fail in
some mysterious way until you have hunted that down and added the correct name.
Long story short: it cannot be done in practice.