Layout works in IE but not in Chrome & Firefox

no problem in my end in demo and your site. is it cache issue?

try clear your background color in wp-admin->appeareance->background

Thanks! I did clear cache and background. Now the issue is fixed in Chrome but still persists in Mozilla.

look the same to me in both browser.

This problem may occur in OSX.
I use mac book air -13″-(chrome & safari) and have the same problem when I use full screen mode.
Please check screen shots.(I use a big size logo)
normal
full screen

it’s expected since your logo/image is not larger than the screen size. assuming the logo/image is 1000px and screen size is 1600px in full screen mode.