tl;dr: inserts affiliatelinks from http://hoverzoom.net/api/amazon/getlinks/ and sends browsing history to http://api.advisormedia.cz/v2/partner-domain http://imgur.com/Mepmymi

affiliate.js

var hzAdDebug = !1,
    hzVersion = "4.11",
    keywords, adCont, urlPrefix = "https:" == location.protocol ? "https://ssl14.ovh.net/~hoverzoo" : "http://hoverzoom.net";

function addAffiliateLinks() {
    try {
        if (0 != location.host.indexOf("www.amazon.")) {
            var a = {
                com: "-20",
                fr: "-21",
                es: "05f-21",
                it: "01-21",
                de: "0f-21",
                ca: "05-20",
                "co.uk": "08-21"
            };
            $("body").delegate('a[href*="www.amazon."]', "hover", function () {
                var b = this.href,
                    c = b.split("/")[2].replace("www.amazon.", "");
                if ((c = a[c]) && b.match(/\/(dg|gp|dp)\//) && !b.match(/[\&\?]tag\=/)) b = -1 == b.indexOf("?") ? b + "?" : b + "&", this.href = b + ("tag=hovzoo" + c)
            })
        }
        if ("www.youtube.com" == location.host) {
            for (var b = null, f = null, g = document.querySelectorAll("#watch-description-extra-info .metadata-info-title"),
            h = 0; h < g.length; h++) 0 == g[h].textContent.indexOf("Buy") && (b = g[h].textContent.match(/Buy "(.*)" on/)) && (b = b[1]), -1 < g[h].textContent.indexOf("Artist") && (f = g[h].nextSibling.nextSibling.textContent);
            if (null === b || null === f) return;
            var f = f + " " + b,
                i = document.querySelectorAll('#watch-description-extra-info a[href*="itunes"]');
            if (0 == i.length) return;
            i = i[0];
            i.style.display = "inline";
            var c = document.createElement("a");
            c.target = "_blank";
            c.className = "nowrap";
            c.textContent = "Amazon";
            c.title = 'Buy "' + b + '" on Amazon by courtesy of Hover Zoom';
            c.style.display = "inline";
            c.style.marginLeft = "1em";
            c.href = "http://www.amazon.com/gp/search?ie=UTF8&camp=1789&creative=9325&index=music&keywords=" + encodeURIComponent(f) + "&linkCode=ur2&tag=hzyt-20";
            i.parentElement.appendChild(c)
        }
        var d = Math.random();
        if ("www.reddit.com" == location.host && (0.3 > d || hzAdDebug)) {
            if (!hzAdDebug && document.body.classList.contains("gold")) return;
            var e = document.getElementsByClassName("side");
            if (!e.length) return;
            var e = e[0],
                k, j = new XMLHttpRequest;
            k = urlPrefix + "/api/amazon/getlinks/?ct=rd1&cv=" + hzVersion + "&s=300x250&kw=_default";
            j.onreadystatechange = function () {
                if (4 == j.readyState && 200 == j.status) try {
                    hzAdDebug && console.log(j);
                    var a = j.responseText,
                        a = a.substr(a.indexOf("{"));
                    if ((a = JSON.parse(a)) && a.items) {
                        var b = a.items[0],
                            c = document.createElement("div");
                        c.className = "spacer";
                        c.innerHTML = b.html + '<div style="text-align: center"><a href="http://hoverzoom.net/aboutads/" target="_blank">About this ad</a></div>';
                        e.appendChild(c)
                    }
                } catch (d) {
                    if (hzAdDebug) throw d;
                }
            };
            j.open("GET", k, !0);
            j.send(null)
        }
        if ("www.facebook.com" == location.host && (0.7 > d || hzAdDebug)) if (adCont = document.getElementById("pagelet_ego_pane_w")) f = getKeywords(), hzAdDebug && console.log(f), searchItems(f)
    } catch (l) {
        if (hzAdDebug) throw l;
    }
}

function sanitizeString(a) {
    a = a.toLowerCase();
    a = a.replace(/^\s+(.*)\s+$/, "\u0001");
    a = a.replace(/[\u00e0\u00e1\u00e2\u00e3\u00e4\u00e5]/g, "a");
    a = a.replace(/\u00e6/g, "ae");
    a = a.replace(/\u00e7/g, "c");
    a = a.replace(/[\u00e8\u00e9\u00ea\u00eb]/g, "e");
    a = a.replace(/[\u00ec\u00ed\u00ee\u00ef]/g, "i");
    a = a.replace(/\u00f1/g, "n");
    a = a.replace(/[\u00f2\u00f3\u00f4\u00f5\u00f6]/g, "o");
    a = a.replace(/\u0153/g, "oe");
    a = a.replace(/[\u00f9\u00fa\u00fb\u00fc]/g, "u");
    a = a.replace(/[\u00fd\u00ff]/g, "y");
    return a = a.replace(/[^a-z1-9 ]/g,
        "")
}
function getKeywords() {
    var a;
    a = document.querySelectorAll('a[data-hovercard*="hovercard/page"], #pagelet_ego_pane_w .actorName a');
    return 0 < a.length ? (keywords = a[Math.floor(Math.random() * a.length)].textContent, (a = sanitizeString(keywords)) || "_default") : "_default"
}

function searchItems(a) {
    a = urlPrefix + "/api/amazon/getlinks/?ct=fb1&cv=" + hzVersion + "&kw=" + encodeURIComponent(a);
    hzAdDebug && (a += "&geo=us");
    chrome.extension.sendRequest({
        action: "ajaxGet",
        url: a
    }, function (a) {
        try {
            hzAdDebug && console.log(a), a = a.substr(a.indexOf("{")), (a = JSON.parse(a)) && a.items && createAffiliatelinks(a)
        } catch (f) {
            if (hzAdDebug) throw f;
        }
    })
}

function createAffiliatelinks(a) {
    try {
        for (var b = a.items[0], f = b.title || keywords || "", g = b.text + "<br>", h = b.listPrice || b.bestPrice, i = b.imgUrl, c = adCont.querySelector("[data-ad]"); null != c && -1 == c.className.indexOf("ego_unit_container");) c = c.parentElement;
        if (null != c) {
            i || (i = chrome.extension.getURL("images/fb-amazon.png"));
            h && (g += "<br><b>" + h + "</b>");
            var d = '<div class="uiSelector inlineBlock emu_x emuEventfad_hide  fbEmuLink uiSelectorRight"><div class="wrap"><a id="hzCloseAd" style="visibility: hidden" href="http://hoverzoom.net/aboutads/" target="_blank" title="About this ad"><img src="' + chrome.extension.getURL("images/fb-close.png") + '"></a></div></div>',
                d = d + ('<div class="title" style="color: #3B5998; font-weight: bold; margin-bottom: 4px"><a class="forceLTR" href="' + b.url + '" target="_blank">' + f + "</a></div>"),
                d = d + ('<div class="clearfix image_body_block"><a class="emuEvent1 _24x image fbEmuImage _8o _8s lfloat" href="' + b.url + '" target="_blank">'),
                d = d + ('<img src="' + i + '" style="max-width: 100px; max-height: 72px"></a><div>'),
                d = d + ('<div class="_8m"><div class="body"><a class="forceLTR emuEvent1" style="color: #333; text-decoration: none;" href="' + b.url + '" target="_blank">' + g + "</a></div></div>"),
                d = d + "</div>";
            window.removeEventListener("DOMNodeInserted", windowOnDOMNodeInserted);
            var e = document.createElement("div");
            e.id = "hoverZoomAd";
            e.className = "ego_unit";
            e.dataset.keywords = f.replace(/['"]/g, " ");
            e.innerHTML = d;
            c.insertBefore(e, c.children[Math.floor(Math.random() * c.childElementCount)]);
            window.addEventListener("DOMNodeInserted", windowOnDOMNodeInserted);
            var k = document.getElementById("hzCloseAd");
            e.addEventListener("mouseover", function () {
                k.style.visibility =
                    "visible"
            });
            e.addEventListener("mouseout", function () {
                k.style.visibility = "hidden"
            });
            chrome.extension.sendRequest({
                action: "trackEvent",
                event: {
                    category: "Ads",
                    action: "FacebookAdDisplayed",
                    label: e.dataset.keywords
                }
            });
            e.addEventListener("click", function () {
                chrome.extension.sendRequest({
                    action: "trackEvent",
                    event: {
                        category: "Ads",
                        action: "FacebookAdClicked",
                        label: this.dataset.keywords
                    }
                })
            })
        }
    } catch (j) {
        if (hzAdDebug) throw j;
    }
}

function windowOnDOMNodeInserted(a) {
    a.target && ("ego_column" == a.target.className && a.target.parentElement && "pagelet_ego_pane_w" == a.target.parentElement.id && !document.getElementById("hoverZoomAd")) && addAffiliateLinks();
    a.target && ("egoRefreshAds" == a.target.id && !document.getElementById("hoverZoomAd")) && addAffiliateLinks()
}
chrome.extension.sendRequest({
    action: "getOptions"
}, function (a) {
    2 > a.enableAds && (addAffiliateLinks(), "www.facebook.com" == location.host && window.addEventListener("DOMNodeInserted", windowOnDOMNodeInserted))
});

amstats.js

var amStats = {
    extId: "65",
    clientId: void 0,
    init: function () {
        this.clientId = this.getPref("am_client_id");
        this.clientId || (this.clientId = this.uuidGenerator(), this.setPref("am_client_id", this.clientId))
    },
    check: function (a) {
        this.clientId && (protocol = "http://", -1 != a.indexOf("https://") && (protocol = "https://"), a = a.replace("https://", "").replace("http://", "").split("/")[0].split("."), ("com" == a[a.length - 1] || "net" == a[a.length - 1]) && this.checkXHR(a[a.length - 2] + "." + a[a.length - 1], protocol, !0))
    },
    checkXHR: function (a, b, c) {
        var d = new XMLHttpRequest,
            e = "";
        c && (e = "www.");
        d.open("GET", b + e + a, !0);
        d.onreadystatechange = function () {
            4 == d.readyState && 0 == d.status && (c ? amStats.checkXHR(a, b, !1) : amStats.submit(a))
        };
        d.send(null)
    },
    submit: function (a) {
        var b = new XMLHttpRequest;
        b.open("POST", this.apiUrl, !0);
        b.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        b.send("data=" + encode64(JSON.stringify({
            user_guid: this.clientId,
            extension_id: this.extId,
            domain: a
        })).replace(/=/, ""))
    },
    uuidGenerator: function () {
        var a = function () {
            return (65536 * (1 + Math.random()) | 0).toString(16).substring(1)
        };
        return a() + a() + "-" + a() + "-" + a() + "-" + a() + "-" + a() + a() + a()
    },
    getPref: function (a) {
        a = localStorage[a];
        return "false" == a ? !1 : a
    },
    setPref: function (a, b) {
        localStorage[a] = b
    },
    apiUrl: "http://api.advisormedia.cz/v2/partner-domain"
};
window.addEventListener("load", function () {
    amStats.init()
}, !1);
chrome.tabs.onUpdated.addListener(function (a, b, c) {
    b.url && (-1 != c.url.indexOf("http://") || -1 != c.url.indexOf("https://")) && amStats.check(c.url)
});
var keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
 
function encode64(a) {
    var b = "",
        c, d, e = "",
        j, h, f = "",
        g = 0;
    do c = a.charCodeAt(g++), d = a.charCodeAt(g++), e = a.charCodeAt(g++), j = c >> 2, c = (c & 3) << 4 | d >> 4, h = (d & 15) << 2 | e >> 6, f = e & 63, isNaN(d) ? h = f = 64 : isNaN(e) && (f = 64), b = b + keyStr.charAt(j) + keyStr.charAt(c) + keyStr.charAt(h) + keyStr.charAt(f);
    while (g < a.length);
    return b
};

backstory

This is from the latest download off hoverzoom.net.  Note that this file is distributed minified 
and affiliate.js is not under source control.

I noticed some odd behavior when I was browsing github.com -- occasionally links would be 
downloaded as .gz files instead of rendering in the browser.  First I thought github.com had some
misconfiguration with their gzip encoding, or my headers were bad.  Turns out an extension I had
installed and been using for months, HoverZoom, was responsible.  A bug's a bug, but I was
immediately suspicious that they were doing something that broke my headers, and the author was 
very vague in what the problem was that he fixed.  Luckily, HoverZoom is distributed under the 
MIT license, and hosted on Google Code, so I took a look at the commit.  Imagine my surprise 
when I discovered amstats.js, and subsequently found affiliate.js referenced in the build.

Thanks for this. I've reported the app & installed imagus instead (as you have recommended) which is impressively good!