Used below payload as getElementsbyTagName got H1 and H2's values and modified them.
document.getElementsByTagName('h2')[2].innerHTML = "Modified you";
document.getElementsByTagName('h1')[0].innerHTML = "Found you";
Javascript to change form options
  • Use Firefox webdev toolbar: Go to Forms -> Convert Select Elements To Text Fields, Type in Inject, click submit.
  • Can use Firefox extensions like Live Http Headers, Tamperdata, or Firebug by changing the name being sent.