'Clone the browser br. Cloned browsers are used for multi-threaded
downloads, since mechanize is not thread safe. The default cloning
routines should capture most browser customization, but if you do
something exotic in your recipe, you should override this method in
your recipe and clone manually.
Cloned browser instances use the same, thread-safe CookieJar by
default, unless you have customized cookie handling.'

def clone_browser(self, br):

    if callable(getattr(br, 'clone_browser', None)):
        return br.clone_browser()
    return self.get_browser()
