enigma1 - 12:48 pm on Feb 15, 2012 (gmt 0)
The checkout part is on another site. You're also pulling in various resources from other domains. I haven't checked with each and latest browser version but some of them may issue warnings on external redirects. External resources may also slow down page loading as the browser will have to pull them in. Some people may also filter content outside your domain yet expect to see a functional site.
If possible modify the cart to process the orders inside your site.