function fireMyPopup(popupName) {
<!-- Due to different browser naming of certain key global variables, we need to do three different tests to determine their values -->

// Determine how much the visitor had scrolled

var scrolledX, scrolledY;
if( self.pageYOffset ) {
  scrolledX = self.pageXOffset;
  scrolledY = self.pageYOffset;
} else if( document.documentElement && document.documentElement.scrollTop ) {
  scrolledX = document.documentElement.scrollLeft;
  scrolledY = document.documentElement.scrollTop;
} else if( document.body ) {
  scrolledX = document.body.scrollLeft;
  scrolledY = document.body.scrollTop;
}

// Determine the coordinates of the center of browser's window

var centerX, centerY;
if( self.innerHeight ) {
  centerX = self.innerWidth;
  centerY = self.innerHeight;
} else if( document.documentElement && document.documentElement.clientHeight ) {
  centerX = document.documentElement.clientWidth;
  centerY = document.documentElement.clientHeight;
} else if( document.body ) {
  centerX = document.body.clientWidth;
  centerY = document.body.clientHeight;
}

  var leftOffset = scrolledX + (centerX - 1100) / 2;
  var topOffset = scrolledY + (centerY - 670) / 2;
switch (popupName) {
case "popup1":
  document.getElementById("popup1").style.top = topOffset + "px";
  document.getElementById("popup1").style.left = leftOffset + "px";
  document.getElementById("popup1").style.display = "block";
  //alert("popup1")
break
case "popup2":
  document.getElementById("popup2").style.top = topOffset + "px";
  document.getElementById("popup2").style.left = leftOffset + "px";
  document.getElementById("popup2").style.display = "block";
  //alert("popup2")
break
case "popup3":
  document.getElementById("popup3").style.top = topOffset + "px";
  document.getElementById("popup3").style.left = leftOffset + "px";
  document.getElementById("popup3").style.display = "block";
  //alert("popup3")
break
case "popup4":
  document.getElementById("popup4").style.top = topOffset + "px";
  document.getElementById("popup4").style.left = leftOffset + "px";
  document.getElementById("popup4").style.display = "block";
  //alert("popup4")
break
case "leftpopup1":
  document.getElementById("leftpopup1").style.top = topOffset + "px";
  document.getElementById("leftpopup1").style.left = leftOffset + "px";
  document.getElementById("leftpopup1").style.display = "block";
  //alert("leftpopup")
break
case "leftpopup2":
  document.getElementById("leftpopup2").style.top = topOffset + "px";
  document.getElementById("leftpopup2").style.left = leftOffset + "px";
  document.getElementById("leftpopup2").style.display = "block";
  //alert("leftpopup")
break
default:
alert("undetermined")
}
}