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.