Altering contents when loading iframes
If you wanted to retain any event handlers that were already attached to your elements, you could change the first piece of code like this an avoid one of the dangers of setting innerHTML on an element that already has a bunch of HTML in it:

// add iframes to page
var normal_sortables = document.getElementById('normal-sortables');
// create container div
var newDiv = document.createElement("div");
newDiv.className = "postbox";
// put content into container div
newDiv.innerHTML = '&lt;iframe style="width:100%;height:300px;" id="iframe_upload" src="upload.php"&gt;&lt;/iframe&gt;&lt;iframe style="width:100%;height:300px;" id="iframe_images" src="images.php"&gt;&lt;/iframe&gt;&lt;iframe style="width:100%;height:300px;" id="iframe_pdf_documents" src="pdf.php"&gt;&lt;/iframe&gt;';
// add container div to the sortables
normal_sortables.appendChild(newDiv);