About a year ago, Facebook did away with its extremely restrictive gender options ("male," "female," or nothing). But it would still only let you choose from 58 options (including, for example, "cis male" and "transfeminine"). Now, after receiving much criticism, the social network has finally decided to provide, along with the existing options, a blank field for users to fill in however they see fit.
As for pronouns, though, you can only choose between "him," "her," or "them."
This is what it looks like, though for unknown reasons, it's only available to a small number of users right now: