You can always explicitly send a header -- it doesn't look like you're doing that. CGI.pm makes it easy:

print $q->header('text/html');
[download]

perldoc CGI for more on this. Or, you can send your header manually:

print "Content-type: text/html\n\n";
[download]

Other than that, I'm not sure why the Mozilla browsers aren't rendering the code. Perhaps posting the contents of the $page variable or the *.rs files would help.