This product does much more than HTTP/HTTPS filtering, thus assuming blocking facebook would not work, it will still not be totally wasted isn't it
Joke aside, I just can't believe you really tried to find some existing solution at least within this forum.
I just typed "facebook" in the search section and found 63 posts related to something similar to your question.
OK, some are not in English...
Anyway, adding facebook.com in the list of denied domains will block it, this is as simple as this. It obviously assumes you are not using transparent but explicit proxy. If you use transparent proxy, thne you can block HTTP access to facebook but not HTTPS, at least using proxy features.
Then you may try to implement some workarounds. This has been discussed at length in this forum.
I know search engine is not very powerful but it nevertheless should help you.