The facebook URL field on user profiles is now editable directly by users. Users who save a value will have the value displayed publicly on their OzBargain user page.
The field has been non-editable since we implemented Facebook logins, and during the sign-up process we asked users if they wanted to display a link to their facebook page on their OzBargain user profile. However, Facebook is now returning a non-direct, app-only URL which is not the same as the user's facebook profile URL. So for those users who have opted in to display their facebook URL and the link was a usable, direct link before the Facebook changes, we've retained those values for display, but discarded the non-direct ones.
Going forward, users who have never linked their facebook account and opted-in to display their facebook profiles will have to manually save their facebook profile URL in their user profile if they want them to be displayed. To do so, go to My Account -> Settings, then the profile tab.
On a semi-related note, we will be removing Google+ profile URLs from our system very soon since Google is shutting down Plus. Google sign-ins will continue to work.