Index: lib/io.js
diff --git a/lib/io.js b/lib/io.js
index 6a07389c6f2eafec04176b87cf46de1cacbd17c6..4b352d0036d40e65157666ba728ddd84e2420101 100644
--- a/lib/io.js
+++ b/lib/io.js
@@ -15,6 +15,8 @@
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+"use strict";
+
 const keyPrefix = "file:";
 
 function fileToKey(file)
@@ -26,7 +28,7 @@ function loadFile(file, successCallback, errorCallback)
 {
   let key = fileToKey(file);
 
-  ext.storage.get([key], function(items)
+  ext.storage.get([key], items =>
   {
     let entry = items[key];
 
@@ -51,12 +53,9 @@ function saveFile(file, data, callback)
 
 exports.IO =
 {
-  resolveFilePath: function(path)
-  {
-    return new FakeFile(path);
-  },
+  resolveFilePath(path) { return new FakeFile(path); },
 
-  readFromFile: function(file, listener, callback)
+  readFromFile(file, listener, callback)
   {
     function onLoaded(entry)
     {
@@ -70,12 +69,12 @@ exports.IO =
     loadFile(file, onLoaded, callback);
   },
 
-  writeToFile: function(file, data, callback)
+  writeToFile(file, data, callback)
   {
     saveFile(file, data, callback);
   },
 
-  copyFile: function(fromFile, toFile, callback)
+  copyFile(fromFile, toFile, callback)
   {
     function onLoaded(entry)
     {
@@ -85,11 +84,11 @@ exports.IO =
     loadFile(fromFile, onLoaded, callback);
   },
 
-  renameFile: function(fromFile, newName, callback)
+  renameFile(fromFile, newName, callback)
   {
     function onLoaded(entry)
     {
-      ext.storage.remove(fileToKey(fromFile), function()
+      ext.storage.remove(fileToKey(fromFile), () =>
       {
         ext.storage.set(keyPrefix + newName, entry, callback);
       });
@@ -98,12 +97,12 @@ exports.IO =
     loadFile(fromFile, onLoaded, callback);
   },
 
-  removeFile: function(file, callback)
+  removeFile(file, callback)
   {
     ext.storage.remove(fileToKey(file), callback);
   },
 
-  statFile: function(file, callback)
+  statFile(file, callback)
   {
     function onLoaded(entry)
     {