As you can see, your first name is shown in this article(only when you are logged in). The plugin Getcbfield can show a field from community builder. Download the file and install it as a Joomla! plugin. Under parameters the field to be shown can be selected. The firstname is shown by default. Can only be used when Community Builder is installed.
Customized fields can also be used. Place getcbfield in sprockeds in your content, the specified field will be shown.