There are a few products, typically hardware based, which can do this. If you are looking for "cheap" or "free" - that may be a different problem.

The product category you are looking for is a "next generation" firewalls. Sophos, Checkpoint, Barracuda, PaloAlto, have these products to varying degrees, some of them can be used to do what you want. IIRC the Sophos CyberRoam can do exactly "If *.facebook.com Then Apply Rate X"

Most of them are really dumb, creating a dynamic address group based on DNS names which it struggles to keep relevant. Many are not smart enough to deduce adjacent content ( e.g. Twitter.com vs their photos hosting vs their CDN ) which means its basically useless.

The other approach, which may be possible depending on the product, is using signature based policies in the IDS, IPS and content categorization engines in these products. So in other words, there may be a content category, like "Facebook and related stuff" which perhaps you can use in a bandwidth policy.

The difficulty is that rate shaping facebook.com, naively, is not effective.

To convince yourself, take wireshark, and capture a session where you do facebook stuff. You will find that many of the ancillary domains accessed are not facebook.com - and often these are where the bandwidth is begin consumed. When you get to the CDN side of thing, some of these are just a mess.

( PS: I write a traffic shaping system in 1999 that did exactly what you wanted, it was a technical achievement, but about 10 years too early - the market just wanted to block NAPSTER. But I am familiar with the challenges, and keep up on the players in this space. I would say focus less on the specific solution and on the problem. What problem are you solving? "Slowing Facebook" is a solution - there may be other solutions to solve your problem. )