title: Change content of a webpage dynamically with a Firefox extension using Javascript without Greasemonkey
body: <p>I'd like to change the content of webpages to put an element that changes according to the webpage.</p>
  
  <p>e.g. I'd like to display a div element with the text "You are on <a href="http://www.google.com" rel="noreferrer">http://www.google.com</a>" when a user is on the website <a href="http://www.google.com" rel="noreferrer">http://www.google.com</a> but when a user goes to <a href="http://www.yahoo.com" rel="noreferrer">http://www.yahoo.com</a> the div should change and display "You're on <a href="http://www.yahoo.com" rel="noreferrer">http://www.yahoo.com</a>".</p>
  
  <p>What I'm looking for is some kind of example to begin with (I hope not being the first person to think of this kind of trick).  </p>