How to access a document's HTML in Firefox using IAccessible

I can get an IAccessible object from a Firefox window using this code:

Guid guid = new Guid("{618736E0-3C3D-11CF-810C-00AA00389B71}");
object obj = null;
int ret = AccessibleObjectFromWindow(hWnd, 
    (uint) OBJID.WINDOW, ref guid, ref obj);
Accessibility.IAccessible acc = (Accessibility.IAccessible)obj;

However, I'm not sure where to go from here. I need to get the full HTML from the document. I know about the IAccessible.get_accValue() method, but I'm not really sure how to use it in relation to Firefox. Any help would be much appreciated.

Solution

Apparently you can't get the full HTML source using IAccessible. I found this but it doesn't work in FF3.5:

IServiceProvider *pServProv = NULL;
pAccessible->QueryInterface(IID_IServiceProvider, (void**)&pServProv);
ISimpleDOMNode *pSimpleDOMNode;
if (pServProv) {
  const GUID refguid = {0x0c539790, 0x12e4, 0x11cf, 0xb6, 0x61,
                        0x00, 0xaa, 0x00, 0x4c, 0xd6, 0xd8};
  HRESULT result = pServProv->QueryService(refguid, IID_ISimpleDOMNode,
                                           (void**)&pSimpleDOMNode);
  if (SUCCEEDED(hresult) && pSimpleDOMNode != NULL) {
    /* This is a Mozilla node! Use special ISimpleDOMNode methods described in
      ISimpleDOMNode.idl. */
  }
}

I also found this, which doesn't work in FF3.5 either:

HRESULT hr = AccessibleObjectFromWindow(hwnd, OBJID_CLIENT,
      IID_IAccessible, (void**)&pAccessible);
if (SUCCEEDED(hr) && pAccessible != NULL) {
HRESULT hr = pAccessible->QueryInterface(
      IID_ISimpleDOMNode, (void**)&pSimpleDOMNode);
}

I'm stuck. :(