How can external app get current Firefox URL?

I posted the question below on Friday but haven't had any replies.  Is
this the right place to post this question?  If not, any suggestions for
where else I might post it?

BTW I mostly work in C using the Win32 API so if anyone has an example
using that I'd sure appreciate it.

Thanks.

-Barry

......................

In Windows, how can an external app get the currently-displayed URL in
Firefox?

The current-page URL cannot be fetched from any displayed control.  The
displayed URL is not in a "real" control.  This is the case in Mozilla
too, but Mozilla has a handy hidden edit control where this is stashed,
all I have to do is grab the contents of that hidden edit control.
Unfortunately Firefox does not seem to have this hidden edit control so
I need a new solution.

Installing an extension or plugin isn't an option.  Is there perhaps a
message I can sent to the Firefox window that will return its current
URL?