Issue with site header in firefox

I've been working on a new theme for my wordpress website and after some tinkering everything looks and works fine except for my header. When I open the website In firefox the header goes to It's full size and it ends up being too big while In other browsers It Is fine.

I've been googling solutions but none seem to work for me. Can anyone help me out so that firefox users won't get a big banner slapped in their faces?

Thanks In advance.

Link to my website