Messes up header while loading

Works well on my site: http://l7world.com/
But in firefox, the image appears for a moment at the center top with a white background the height of the image floated and the width of the content of blog appears. Background disappears when image floats left.

Any solution to stop messy appearance while loading in firefox?

http://ww.wp.xz.cn/extend/plugins/wp-float/