site jumps up when loaded

Hey, this is a quick fix I’m sure, but I just can’t figure it out.

My site is https://simplythreemusic.com. When I first load the main page on my iPhone 4s or Firefox, the slider and main page are further down on the page. When the site fully loads, it jumps up to where it should be.

Why is it doing this? How can I stop it from doing this jump?

Zack