Doesn't happen in FF 126.96.36.199 on my computer - the menu stays centered just fine with About page, portfolio, and landcape and portrait images.
I agree that there might be some room for negative vertical space at the top of the page, especially around the menu. Otherwise this is much better than the earlier incarnation. Simple is beautiful! And so are the photographs; I especially like Canal Cedar Island as that reminds me of Finland.
A design comment: right now the incentive to click on your images is for people to know the price or get some text on those images. If you included larger images on the individual photo page, they would have more incentive to click. This way you'd get more information on which images are most compelling - which might be useful marketing info for you!