1) Create a new bookmark
2) Edit it's properties. Paste the following (single-line) code into it.

javascript:c=document.getElementsByTagName("HTML")[0].outerHTML;t=document.body.appendChild(document.createElement('<textarea%20style="width:96%;height:50em;z-index:100;position:absolute;top:1em;left:1em; border:3px%20outset%20black;%20background-color:#eeeeee"%20ondblclick="this.removeNode(true)">'));t.value=c;alert('Double-click%20textarea%20to%20remove.');

3) Click the bookmark on a page to see the post-DHTML HTML in a big copyable textarea.
4) Double-click the text area to return the page to its virgin state.