Need Help Regarding “Serve static content from a cookieless domain”

I just installed "Page Speed" browser addon from Google that works with "FireBug" addon.

When I open my site www.decentbanners.com FireBug scans the site performance and show the result and also suggest what steps should be taken to increase the site loading speed.

One of the suggestion it is showing is

"Serve static content from a cookieless domain"

It is saying

Need Help Regarding "Serve static content from a cookieless domain"