how to send html with mailto?

how to send html with mailto?

I have the following html form...
<form id="mform" method="get" enctype="text/plain">
<input name="firstname" type="text" id="firstname">
<input type="submit" class="submit-sponsor-btn" name="submit"
value="Submit" onclick="javascript:doMailto(); return false;"
id="submit">
</form>
and my javascript looks like this...
var msubject = "Become an AgCN sponsor to start your connection to future
talent";
var mfirstname = $('#firstname').val();
var mbody = "<h1>AgCN Sponsor Information
Below:</h1><p>Firstname:"+mfirstname + "</p>";
var mrecipient = "friendsklp@gmail.com";
var sMailto = "mailto:klewis@ffa.org?subject="+ msubject + "&body="+ mbody;
function doMailto() {
window.open(sMailto);
}
What do I need to do with this code, to enable HTML tags to be rendered
within the e-mail? Because as of right now, it simply shows the element
tags along with the content.
Thanks for any advice!