<br /><b>Notice</b>: Undefined variable: firstname in <b>C:\xampp\htdocs\dl\index.php</b> on line <b>66</b><br />
You're calling a variable
$firstname on line 66 of your file index.php and it hasn't been declared before use.
Without seeing further code, it's difficult to advise further.
What is mostlikely happening is that your variable probably does not get set upon the loading of your page. Try setting your variable to an initial value and then let the code update it when it is run.
<?php $firstname=" "; //whatever code in here that sets the value of your variable to something else //$firstname= "Mike" ?>