Safari VS Firefox with Clean Retina

Hi guys!

I am working with Safari in order to build my CR-based web site. To my huge surprise, a friend, who is using Firefox, told me that my header image was “all wrong” on my home page. After checking, he is of course right. My header image is properly centered with Safari but totally positioned to the left with Firefox.

Is there something I can do to correct that problem?

Fot those who want to browse the difference: https://joseeblanchette.ca

Thanks!

Francois

PS: I am using a custom CSS code in order to get rid of the image in sub-pages (if it might help to diagnostic the problem…)