Amazon is targetting Firefox with a bad technique https://bugzilla.mozilla.org/show_bug.cgi?id=1172205 Mozilla fixed a bug but as of today Amazon didn't change yet their script.

amazon-prefetch.js

amznJQ.available("jQuery", function() {
    jQuery(window).load(function() {
        setTimeout(function() {
            var imageAssets = new Array();
            var jsCssAssets = new Array();
            imageAssets.push("https://images-fe.ssl-images-amazon.com/images/G/09/x-locale/common/buy-buttons/review-1-click-order._CB171143523_.gif");
            imageAssets.push("https://images-fe.ssl-images-amazon.com/images/G/09/x-locale/common/buttons/continue-shopping._CB192262037_.gif");
            imageAssets.push("https://images-fe.ssl-images-amazon.com/images/G/09/x-locale/common/buy-buttons/thank-you-elbow._CB192261665_.gif");
            imageAssets.push("https://images-fe.ssl-images-amazon.com/images/G/09/x-locale/communities/social/snwicons_v2._CB383421867_.png");
            imageAssets.push("https://images-fe.ssl-images-amazon.com/images/G/09/checkout/assets/carrot._CB192555707_.gif");
            imageAssets.push("https://images-fe.ssl-images-amazon.com/images/G/09/checkout/thank-you-page/assets/yellow-rounded-corner-sprite._CB192555699_.gif");
            imageAssets.push("https://images-fe.ssl-images-amazon.com/images/G/09/checkout/thank-you-page/assets/white-rounded-corner-sprite._CB212531219_.gif");
            jsCssAssets.push("https://images-na.ssl-images-amazon.com/images/G/01/browser-scripts/jp-site-wide-css-beacon/site-wide-6800426958._V1_.css");
            jsCssAssets.push("https://images-na.ssl-images-amazon.com/images/G/01/browser-scripts/site-wide-js-1.2.6-beacon/site-wide-3750999928._V1_.js");

            // pre-fetching image assets
            for (var i = 0; i < imageAssets.length; i++) {
                new Image().src = imageAssets[i];
            }
            // pre-fetching css and js assets based on different browser types
            var isIE = /*@cc_on!@*/ 0;
            var isFireFox = /Firefox/.test(navigator.userAgent);
            if (isIE) {
                for (var i = 0; i < jsCssAssets.length; i++) {
                    new Image().src = jsCssAssets[i];
                }
            } else if (isFireFox) {
                for (var i = 0; i < jsCssAssets.length; i++) {
                    var o = document.createElement("object");
                    o.data = jsCssAssets[i];
                    o.width = o.height = 0;
                    document.body.appendChild(o);
                }
            }
        }, 2000);
    });
});