The background appears in this header.

According to the css specification, a fixed background image of any box should be fixed with respect to the canvas. CSS1 paragraph 5.3.5:

If a background image is specified, the value of 'background-attachment' determines if it is fixed with regard to the canvas or if it scrolls along with the content.

This is correct in this page, where this value is set to 'fixed'. The problem is with the background-repeat property. This is set to 'no-repeat' here. This normally works when it is specified for the <body> element, but not if it is overridden in a subelement, such as <h1> in this page. Only for a very small canvas size, should the image be visible in this page. However it is visible for all canvas sizes.

Mozilla does handle this correctly.