WordPress init action not working on Firefox?

I have added following Function in functions.php

themes -> mytheme -> functions.php


   <?php
        function testfunc() 
        {
             echo "Test Function";
             exit;
        }
        add_action( 'init', 'testfunc' );
    ?>

on chrome and safari browser its working fine. but in Firefox browser its not working properly.

on local-host all things are working fine in Firefox but its not working on live server.