I went to Vice's fb page, found the same post that OP linked to and checked the URL. The pfbid part is exactly the same to me. The URL by default has some additional params attached like __cft__ and __tn__, which can be stripped, and those are probably tracking-related. Based on this, I don't think that pfbid is connected to tracking
If I were Meta, this is how I would implement this. First, get everyone used to the new opaque base64 encoded blob, by using it just like the previous numeric post id. Then, after all the initial speculation dies down, encode other stuff in it.
