nsIWebBrowserPersist saveDocument() method

Dear Concerned,

I am using mozilla interface nsIWebBrowserPersist (https://
developer.mozilla.org/en/XPCOM_Interface_Reference/
nsIWebBrowserPersist) with a method called saveDocument().

I have integrated this one with mozrepl. So if I give repl.save() it
is saving the page.

But the problem is it saves the html without any image. But as per
specification it is to save the specified DOM document to file and
optionally all linked files (e.g. images, CSS, JS & subframes).

Please note that I have also given a delay loop in javascript.

Do you have any advice? Am I missing something?

Thanks
Nashid