[ksa]

Volun, как вариант...

<form method="post" id="form_name">
	<input name="first_name" placeholder="First Name" class="form-control" data-i18n="">
	<input  name="last_name" placeholder="Last Name" class="form-control" data-i18n="">
	<input  name="email" placeholder="Email" class="form-control" data-i18n="" value='tmp@test.ru'>
	<button type="submit" id="btn_name" class="btn-formnav btn"><span data-animation-name="next-span"><span data-i18n="">NEXT</span> &gt;</span></button>
</form>
<br>
<form method="post" id="form_pass">
	<input name="password" placeholder="Password" class="form-control" data-i18n="">
	<input  name="pass_conf" placeholder="Confirm Password" class="form-control" data-i18n="">
	<input name="hidden_email" class="form-control" data-i18n="" style="display: none;">
	<button type="submit" id="btn_pass" class="btn-formnav btn"><span data-animation-name="next-span"><span data-i18n="">NEXT</span> &gt;</span></button>
</form>
<script type='text/javascript'>
	var oi=document.querySelector('#form_name [name="email"]');
	var o=document.querySelector('#form_pass [name="hidden_email"]');
	o.value=oi.value;
	document.querySelector('#btn_pass').click();
</script>