favicon_link_tag 'mb-icon.png', rel: 'apple-touch-icon', type: 'image/png'
<link href="/assets/mb-icon.png" rel="apple-touch-icon" type="image/png" />

<%= favicon_link_tag 'favicon.ico' %>
<%= favicon_link_tag 'apple-icon.jpeg', rel: 'apple-touch-icon', type:'image/jpeg' %>

<link href="/assets/favicon.ico" rel="shortcut icon" type="image/vnd.microsoft.icon">
<link href="/images/apple-icon.jpeg" rel="apple-touch-icon" type="image/jpeg">