Well, it's not completely impossible, but you're going to have to use a very powerful utility to do something rather trivial, and it's not a one-step setup.
The Workflow app can create automated scripts to do some amazing things. One small thing it can do is launch an app. And it can do so from a icon it creates on the home screen (using Safari's ability to create links on home screens). It can even be made to look a little bit like the FaceBook icon.
But it does take a few seconds longer to launch, since it has another app and a script to run before it can launch FaceBook.
It seems like a lot of trouble to do something that, as dhewson777 pointed out, has little utility; but if you really need it and are willing to buy the Workflow app to make it happen, I'll talk you through the setup.
There might be a simpler, cheaper, or even free app that will do the same thing, but I haven't heard of it.