You can't do that with a custom field, they always show up under 'Additional Information'.
You can add your own html in the template that makes it appear under Additional Contact Information; so it will show a xFire box where members can fill in their name; and with a plugin you can update the field whenever a member edits his/her profile.
Edit:
Try this;
Install:
Upload xfire.php into your ./inc/plugins/ folder
Go to your PluginManager and Activate the "xFire Name In UserCP Options" Plugin.
What?:
* Add a new box when you press "Edit Profile" in your UserCP. When pressing "Update Profile", the xFire name gets updated ...
* In the MemberProfile there's a new row added under "<username>'s Contact Details", if the user has filled in a xFire name, it will be displayed.
* xFire name is displayed in the postbit if the user has filled one in.
You can add your own html in the template that makes it appear under Additional Contact Information; so it will show a xFire box where members can fill in their name; and with a plugin you can update the field whenever a member edits his/her profile.
Edit:
Try this;
Install:
Upload xfire.php into your ./inc/plugins/ folder
Go to your PluginManager and Activate the "xFire Name In UserCP Options" Plugin.
What?:
* Add a new box when you press "Edit Profile" in your UserCP. When pressing "Update Profile", the xFire name gets updated ...
* In the MemberProfile there's a new row added under "<username>'s Contact Details", if the user has filled in a xFire name, it will be displayed.
* xFire name is displayed in the postbit if the user has filled one in.