is_page() used to disable header image not working on FireFox

I have suppressed the header image on my photo gallery page, http://thetwobyres.co.uk/photos by using an is_page() condition in my header.php.
I am using Twenty Eleven and have created a child theme, with the header.php.

<?php
// Check to see if the header image has been removed - added the is_page condition
     $header_image = get_header_image();
     if ( ! empty( $header_image ) && (! is_page('photos') ) ) :
?>

This works in Safari and IE, but not in FireFox where the header image still shows up.
Any suggestions appreciated.