Bug 77834: Fix problem where form control state is being restored to the wrong form control or not restored at all when going back and forth through session history.  The problem was that the hash key we used was the content ID, which was not consistent from page load to page load.  The fix was to key instead by index of form in document / index of control in form, with logic to fall back to content ID if we are unable to do this. r=nisheeth@netscape.com, sr=jst@netscape.com, a=drivers@mozilla.org (blizzard@mozilla.org)