diff -r 000000000000 -r 6474c204b198 toolkit/webapps/WebappsIconHelpers.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/webapps/WebappsIconHelpers.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,101 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const DEFAULT_ICON_URL = "chrome://global/skin/icons/webapps-64.png";
+
+/**
+ * This function receives a list of icon sizes
+ * and URLs and returns the url string for the biggest icon.
+ *
+ * @param aIcons An object where the keys are the icon sizes
+ *               and the values are URL strings. E.g.:
+ *               aIcons = {
+ *                 "16": "http://www.example.org/icon16.png",
+ *                 "32": "http://www.example.org/icon32.png"
+ *               };
+ *
+ * @returns the URL string for the largest specified icon
+ */
+function getBiggestIconURL(aIcons) {
+  if (!aIcons) {
+    return DEFAULT_ICON_URL;
+  }
+
+  let iconSizes = Object.keys(aIcons);
+  if (iconSizes.length == 0) {
+    return DEFAULT_ICON_URL;
+  }
+  iconSizes.sort(function(a, b) a - b);
+  return aIcons[iconSizes.pop()];
+}
+
+// Download an icon using either a temp file or a pipe.
+function downloadIcon(aIconURI) {
+  let deferred = Promise.defer();
+
+  let mimeService = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+  let mimeType;
+  try {
+    let tIndex = aIconURI.path.indexOf(";");
+    if("data" == aIconURI.scheme && tIndex != -1) {
+      mimeType = aIconURI.path.substring(0, tIndex);
+    } else {
+      mimeType = mimeService.getTypeFromURI(aIconURI);
+     }
+  } catch(e) {
+    deferred.reject("Failed to determine icon MIME type: " + e);
+    return deferred.promise;
+  }
+
+  function onIconDownloaded(aStatusCode, aIcon) {
+    if (Components.isSuccessCode(aStatusCode)) {
+      deferred.resolve([ mimeType, aIcon ]);
+    } else {
+      deferred.reject("Failure downloading icon: " + aStatusCode);
+    }
+  }
+
+  try {
+#ifdef XP_MACOSX
+    let downloadObserver = {
+      onDownloadComplete: function(downloader, request, cx, aStatus, file) {
+        onIconDownloaded(aStatus, file);
+      }
+    };
+
+    let tmpIcon = Services.dirsvc.get("TmpD", Ci.nsIFile);
+    tmpIcon.append("tmpicon." + mimeService.getPrimaryExtension(mimeType, ""));
+    tmpIcon.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, parseInt("666", 8));
+
+    let listener = Cc["@mozilla.org/network/downloader;1"]
+                     .createInstance(Ci.nsIDownloader);
+    listener.init(downloadObserver, tmpIcon);
+#else
+    let pipe = Cc["@mozilla.org/pipe;1"]
+                 .createInstance(Ci.nsIPipe);
+    pipe.init(true, true, 0, 0xffffffff, null);
+
+    let listener = Cc["@mozilla.org/network/simple-stream-listener;1"]
+                     .createInstance(Ci.nsISimpleStreamListener);
+    listener.init(pipe.outputStream, {
+        onStartRequest: function() {},
+        onStopRequest: function(aRequest, aContext, aStatusCode) {
+          pipe.outputStream.close();
+          onIconDownloaded(aStatusCode, pipe.inputStream);
+       }
+    });
+#endif
+
+    let channel = NetUtil.newChannel(aIconURI);
+    let { BadCertHandler } = Cu.import("resource://gre/modules/CertUtils.jsm", {});
+    // Pass true to avoid optional redirect-cert-checking behavior.
+    channel.notificationCallbacks = new BadCertHandler(true);
+
+    channel.asyncOpen(listener, null);
+  } catch(e) {
+    deferred.reject("Failure initiating download of icon: " + e);
+  }
+
+  return deferred.promise;
+}