<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css" />
<style>
{literal}
.facebook_login_a {
display: inline-block;
position: relative;
overflow: hidden;
line-height: 31px;
border-radius: 3px;
background-color: #D34A2E;
color: #FFF;
border: 1px solid #D34A2E;
box-sizing: border-box;
float: left;
margin-top: 10px;
}
.facebook_login_a:hover {
background-color: #D55338;
}
.facebook_login_a i {
border-right: 1px solid #c3452b;
line-height: 31px;
padding-right: 6px;
box-sizing: border-box;
}
{/literal}
</style>
<button class="facebook_login_a" onclick="window.location = '{$link_redirect_fb}'">
<i class="fa fa-facebook"></i> {l s='Login with Facebook' mod='phfacebooklogin'}
</button>
$this->context->link->getModuleLink('phfacebooklogin', 'redirect', array(
'redirect' => urlencode($this->context->cart->getProducts() ?
(Tools::getValue('back') ? Tools::getValue('back') : $this->context->link->getPageLink('order'))
: _PS_BASE_URL_SSL_.$_SERVER['REDIRECT_URL'])
))