diff --git a/mobile/android/base/webapp/EventListener.java b/mobile/android/base/webapp/EventListener.java
index a1091a7cda6f..08777a9f5e05 100644
--- a/mobile/android/base/webapp/EventListener.java
+++ b/mobile/android/base/webapp/EventListener.java
@@ -8,12 +8,15 @@ package org.mozilla.gecko.webapp;
 import org.mozilla.gecko.ActivityHandlerHelper;
 import org.mozilla.gecko.AppConstants;
 import org.mozilla.gecko.GeckoAppShell;
+import org.mozilla.gecko.GeckoEvent;
 import org.mozilla.gecko.GeckoProfile;
 import org.mozilla.gecko.favicons.decoders.FaviconDecoder;
 import org.mozilla.gecko.gfx.BitmapUtils;
 import org.mozilla.gecko.util.ActivityResultHandler;
 import org.mozilla.gecko.EventDispatcher;
-import org.mozilla.gecko.util.GeckoEventListener;
+import org.mozilla.gecko.util.EventCallback;
+import org.mozilla.gecko.util.NativeEventListener;
+import org.mozilla.gecko.util.NativeJSObject;
 import org.mozilla.gecko.util.ThreadUtils;
 import org.mozilla.gecko.WebappAllocator;
 
@@ -30,15 +33,15 @@ import android.net.Uri;
 import android.util.Log;
 
 import java.io.File;
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
-import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
 
-public class EventListener implements GeckoEventListener {
+public class EventListener implements NativeEventListener  {
 
     private static final String LOGTAG = "GeckoWebappEventListener";
 
@@ -63,10 +66,10 @@ public class EventListener implements GeckoEventListener {
     }
 
     @Override
-    public void handleMessage(String event, JSONObject message) {
+    public void handleMessage(String event, NativeJSObject message, EventCallback callback) {
         try {
             if (AppConstants.MOZ_ANDROID_SYNTHAPKS && event.equals("Webapps:InstallApk")) {
-                installApk(GeckoAppShell.getGeckoInterface().getActivity(), message.getString("filePath"), message.getString("data"));
+                installApk(GeckoAppShell.getGeckoInterface().getActivity(), message, callback);
             } else if (event.equals("Webapps:Postinstall")) {
                 if (AppConstants.MOZ_ANDROID_SYNTHAPKS) {
                     postInstallWebapp(message.getString("apkPackageName"), message.getString("origin"));
@@ -94,12 +97,12 @@ public class EventListener implements GeckoEventListener {
 
                 JSONObject obj = new JSONObject();
                 obj.put("profile", preInstallWebapp(name, manifestURL, origin).toString());
-                EventDispatcher.sendResponse(message, obj);
+                callback.sendSuccess(obj);
             } else if (event.equals("Webapps:GetApkVersions")) {
                 JSONObject obj = new JSONObject();
                 obj.put("versions", getApkVersions(GeckoAppShell.getGeckoInterface().getActivity(),
-                                                   message.getJSONArray("packageNames")));
-                EventDispatcher.sendResponse(message, obj);
+                                                   message.getStringArray("packageNames")));
+                callback.sendSuccess(obj);
             }
         } catch (Exception e) {
             Log.e(LOGTAG, "Exception handling message \"" + event + "\":", e);
@@ -180,25 +183,27 @@ public class EventListener implements GeckoEventListener {
         }
     }
 
-    public static void installApk(final Activity context, String filePath, String data) {
-        // This is the data that mozApps.install sent to Webapps.jsm.
-        JSONObject argsObj = null;
+    public static void installApk(final Activity context, NativeJSObject message, EventCallback callback) {
+        final JSONObject messageData;
 
         // We get the manifest url out of javascript here so we can use it as a checksum
         // in a minute, when a package has been installed.
         String manifestUrl = null;
+        String filePath = null;
+
         try {
-            argsObj = new JSONObject(data);
-            manifestUrl = argsObj.getJSONObject("app").getString("manifestURL");
+            filePath = message.getString("filePath");
+            messageData = new JSONObject(message.getObject("data").toString());
+            manifestUrl = messageData.getJSONObject("app").getString("manifestURL");
         } catch (JSONException e) {
-            Log.e(LOGTAG, "can't get manifest URL from JSON data", e);
-            // TODO: propagate the error back to the mozApps.install caller.
+            Log.wtf(LOGTAG, "Error getting file path and data", e);
+            callback.sendError("Error getting file path and data: " + e.toString());
             return;
         }
 
         // We will check the manifestUrl from the one in the APK.
         // Thus, we can have a one-to-one mapping of apk to receiver.
-        final InstallListener receiver = new InstallListener(manifestUrl, argsObj);
+        final InstallListener receiver = new InstallListener(manifestUrl, messageData);
 
         // Listen for packages being installed.
         IntentFilter filter = new IntentFilter(Intent.ACTION_PACKAGE_ADDED);
@@ -208,7 +213,7 @@ public class EventListener implements GeckoEventListener {
         File file = new File(filePath);
         if (!file.exists()) {
             Log.wtf(LOGTAG, "APK file doesn't exist at path " + filePath);
-            // TODO: propagate the error back to the mozApps.install caller.
+            callback.sendError("APK file doesn't exist at path " + filePath);
             return;
         }
 
@@ -239,15 +244,9 @@ public class EventListener implements GeckoEventListener {
 
     private static final int DEFAULT_VERSION_CODE = -1;
 
-    public static JSONObject getApkVersions(Activity context, JSONArray packageNames) {
+    public static JSONObject getApkVersions(Activity context, String[] packageNames) {
         Set<String> packageNameSet = new HashSet<String>();
-        for (int i = 0; i < packageNames.length(); i++) {
-            try {
-                packageNameSet.add(packageNames.getString(i));
-            } catch (JSONException e) {
-                Log.w(LOGTAG, "exception populating settings item", e);
-            }
-        }
+        packageNameSet.addAll(Arrays.asList(packageNames));
 
         final PackageManager pm = context.getPackageManager();
         List<ApplicationInfo> apps = pm.getInstalledApplications(0);
diff --git a/mobile/android/modules/WebappManager.jsm b/mobile/android/modules/WebappManager.jsm
index 967a12c98c39..970e2651ba5d 100644
--- a/mobile/android/modules/WebappManager.jsm
+++ b/mobile/android/modules/WebappManager.jsm
@@ -103,7 +103,13 @@ this.WebappManager = {
     sendMessageToJava({
       type: "Webapps:InstallApk",
       filePath: filePath,
-      data: JSON.stringify(aMessage),
+      data: aMessage,
+    }, (data, error) => {
+      if (!!error) {
+        aMessage.error = error;
+        aMessageManager.sendAsyncMessage("Webapps:Install:Return:KO", aMessage);
+        debug("error downloading APK: " + error);
+      }
     });
   }).bind(this)); },
 
@@ -493,7 +499,7 @@ this.WebappManager = {
         sendMessageToJava({
           type: "Webapps:InstallApk",
           filePath: apk.filePath,
-          data: JSON.stringify(msg),
+          data: msg,
         });
       }
     } else {