partner-contact/partner_firstname/res_user_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
  <data>
    <record id="view_users_form" model="ir.ui.view">
      <field name="name">res.users.form.firstname</field>
      <field name="model">res.users</field>
      <field name="inherit_id" ref="base.view_users_form"/>
      <field name="arch" type="xml">
        <field name="name" position="attributes">
          <attribute name="readonly">False</attribute>
        </field>
      </field>
    </record>
  </data>
</openerp>