Mozilla - how to load a TAB with document previously acquired through gBrowser.contentDocument?

I'm developing an easy Mozilla Firefox extension (FF 5.0 and above), and I need a manner in which I can get the content document from a tab, for example:

<JavaScript function called from XUL document>
var content_1 = gBrowser.contentDocument;

and the goal is to put that content again in another tab, for example:

Application.activeWindow.activeTab.contentDocument = content_1;

but that's not working becasue content.document or contentDocument are read-only.

I mean, instead of getting the URL and reloading the page, I would like to the the tab's content itself and then assign it to another tab.

I'd also like to find a way to get the content of a tab including text filled in by a开发者_Go百科 user in HTML textboxes or wherever in the document, for example, a forum post text before sending it. I'm not sure this last thing is possible whithout having to read the memory or complicating too much the thing...

---

You cannot change contentDocument but you can change document contents. In particular, you can replace the document's root node. This should do:

var targetDoc = Application.activeWindow.activeTab.contentDocument;
var newRoot = targetDoc.importNode(content_1.documentElement, true);
targetDoc.replaceChild(newRoot, targetDoc.documentElement);

When I tried this copied document's contents including dynamic information like textbox input.