<?xml version="1.0" encoding="UTF-8"?>
<openerp>
  <data>
    <report
      auto="False"
      file="account_invoice_webkit/report/account_invoice_webkit.mako"
      id="account_invoice_webkit"
      model="account.invoice"
      name="account.invoice.webkit"
      report_type="webkit"
      string="WebKit Invoice"/>
  </data>
</openerp>

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
  <data>
    <report
      auto="False"
      file="account_invoice_webkit/report/account_invoice_webkit.mako"
      id="account_invoice_webkit"
      model="account.invoice"
      name="account.invoice.webkit"
      report_type="webkit"
      string="WebKit Invoice"/>

    <record id="invoice_button_form" model="ir.ui.view">
            <field name="name">account.invoice.button.form</field>
            <field name="model">account.invoice</field>
            <field name="type">form</field>
            <field name="inherit_id" ref="account.invoice_form"/>
            <field name="arch" type="xml">
              <xpath expr="/form/notebook/page[@string='Invoice']/group/group/button[@string='Print Invoice']" position="replace">
                  <button name="%(account_invoice_webkit)d" string="Print Invoice" type="action" icon="gtk-print" states="open,paid,proforma,sale,proforma2"/>
              </xpath>
        </field>
    </record>
  </data>
</openerp>

Print Invoice prints Webkit invoice
[REF] Print Invoice prints Webkit invoice
