Is this some kind of global template that you're working with here? What you're currently doing is forcing the next component in the chain to return a URL, which seems like it probably isn't what you want since the next one in the chain is likely either another autohandler, a dhandler, or a page.
First off, why use frames at all when you're using Mason? You can simply turn the footer into a component that outputs HTML, and call it from the autohandler like so:
<title><% $m->base_comp->attr('title') %></title>
<% $m->call_next() %>
<& /template/footer.comp &>
Come to think of it, I think it's highly likely you'll get caught in some type of endless recursion unless you configure Mason so that it handles only files of type .mhtml, and then have your next component return links to files of type html which wouldn't be handled by Mason.