diff --git a/.babelrc b/.babelrc
new file mode 100644
index 0000000..c13c5f6
--- /dev/null
+++ b/.babelrc
@@ -0,0 +1,3 @@
+{
+  "presets": ["es2015"]
+}
diff --git a/dist/chrome.crx b/dist/chrome.crx
index ce989ae..e5b03c2 100644
Binary files a/dist/chrome.crx and b/dist/chrome.crx differ
diff --git a/dist/chrome.zip b/dist/chrome.zip
index 09a101e..2e04914 100755
Binary files a/dist/chrome.zip and b/dist/chrome.zip differ
diff --git a/dist/firefox.xpi b/dist/firefox.xpi
index 25380a2..7e99718 100644
Binary files a/dist/firefox.xpi and b/dist/firefox.xpi differ
diff --git a/dist/opera.nex b/dist/opera.nex
index ce989ae..e5b03c2 100644
Binary files a/dist/opera.nex and b/dist/opera.nex differ
diff --git a/gulpfile.js b/gulpfile.babel.js
similarity index 74%
rename from gulpfile.js
rename to gulpfile.babel.js
index b72efd3..46a332f 100644
--- a/gulpfile.js
+++ b/gulpfile.babel.js
@@ -1,5 +1,3 @@
-'use strict'
-
 const gulp  = require('gulp')
 const path  = require('path')
 const merge = require('event-stream').merge
@@ -9,7 +7,7 @@ const $     = require('gulp-load-plugins')()
 
 // Tasks
 gulp.task('clean', () => {
-  return pipe('./tmp', [$.clean()])
+  return pipe('./tmp', $.clean())
 })
 
 gulp.task('build', (cb) => {
@@ -35,9 +33,12 @@ gulp.task('test', ['build'], (cb) => {
 })
 
 gulp.task('styles', () => {
-  return pipe('./src/styles/octotree.less',
-    [$.less(), $.autoprefixer({cascade: true})],
-    './tmp')
+  return pipe(
+    './src/styles/octotree.less',
+    $.less(),
+    $.autoprefixer({cascade: true}),
+    './tmp'
+  )
 })
 
 // Chrome
@@ -52,12 +53,13 @@ gulp.task('chrome:js', ['chrome:template'], () => {
 gulp.task('chrome', ['chrome:js'], () => {
   return merge(
     pipe('./icons/**/*', './tmp/chrome/icons'),
-    pipe(['./libs/**/*', './tmp/octotree.*', './src/config/chrome/**/*', '!./src/config/chrome/storage.js'], './tmp/chrome/')
+    pipe(['./libs/**/*', './tmp/octotree.*',  './src/config/chrome/manifest.json'], './tmp/chrome/'),
+    pipe('./src/config/chrome/background.js', $.babel(), './tmp/chrome/')
   )
 })
 
 gulp.task('chrome:zip', () => {
-  return pipe('./tmp/chrome/**/*', [$.zip('chrome.zip')], './dist')
+  return pipe('./tmp/chrome/**/*', $.zip('chrome.zip'), './dist')
 })
 
 gulp.task('chrome:_crx', (cb) => {
@@ -77,24 +79,7 @@ gulp.task('opera', ['chrome'], () => {
 })
 
 gulp.task('opera:nex', () => {
-  return pipe('./dist/chrome.crx', [$.rename('opera.nex')], './dist')
-})
-
-// Safari
-gulp.task('safari:template', () => {
-  return buildTemplate({SAFARI: true})
-})
-
-gulp.task('safari:js', ['safari:template'], () => {
-  return buildJs([], {SAFARI: true})
-})
-
-gulp.task('safari', ['safari:js'], () => {
-  return merge(
-    pipe('./icons/**/*', './tmp/safari/octotree.safariextension/icons'),
-    pipe(['./libs/**/*', './tmp/octotree.js', './tmp/octotree.css',
-      './src/config/safari/**/*', '!./src/config/safari/storage.js'], './tmp/safari/octotree.safariextension/')
-  )
+  return pipe('./dist/chrome.crx', $.rename('opera.nex'), './dist')
 })
 
 // Firefox
@@ -109,8 +94,8 @@ gulp.task('firefox:js', ['firefox:template'], () => {
 gulp.task('firefox', ['firefox:js'], () => {
   return merge(
     pipe('./icons/**/*', './tmp/firefox/data/icons'),
-    pipe(['./libs/**/*', './tmp/octotree.js', './tmp/octotree.css'], './tmp/firefox/data'),
-    pipe(['./src/config/firefox/firefox.js'], './tmp/firefox/lib'),
+    pipe(['./libs/**/*', './tmp/octotree.*'], './tmp/firefox/data'),
+    pipe('./src/config/firefox/firefox.js', $.babel(), './tmp/firefox/lib'),
     pipe('./src/config/firefox/package.json', './tmp/firefox')
   )
 })
@@ -119,20 +104,31 @@ gulp.task('firefox:xpi', (cb) => {
   $.run('cd ./tmp/firefox && cfx xpi --output-file=../../dist/firefox.xpi').exec(cb)
 })
 
+// Safari
+gulp.task('safari:template', () => {
+  return buildTemplate({SAFARI: true})
+})
+
+gulp.task('safari:js', ['safari:template'], () => {
+  return buildJs([], {SAFARI: true})
+})
+
+gulp.task('safari', ['safari:js'], () => {
+  return merge(
+    pipe('./icons/**/*', './tmp/safari/octotree.safariextension/icons'),
+    pipe(
+      ['./libs/**/*', './tmp/octotree.*', './src/config/safari/**/*'],
+      './tmp/safari/octotree.safariextension/'
+    )
+  )
+})
+
 // Helpers
-function pipe(src, transforms, dest) {
-  if (typeof transforms === 'string') {
-    dest = transforms
-    transforms = null
-  }
-
-  let stream = gulp.src(src)
-  transforms && transforms.forEach(function (transform) {
-    stream = stream.pipe(transform)
-  })
-
-  if (dest) stream = stream.pipe(gulp.dest(dest))
-  return stream
+function pipe(src, ...transforms) {
+  return transforms.reduce((stream, transform) => {
+    const isDest = typeof transform === 'string'
+    return stream.pipe(isDest ? gulp.dest(transform) : transform)
+  }, gulp.src(src))
 }
 
 function html2js(template) {
@@ -171,16 +167,20 @@ function buildJs(overrides, ctx) {
   ].concat(overrides)
    .concat('./src/octotree.js')
 
-  return pipe(src, [
-    $.babel({presets: ['es2015']}),
+  return pipe(
+    src,
+    $.babel(),
     $.concat('octotree.js'),
     $.preprocess({context: ctx}),
-  ], './tmp')
+    './tmp'
+  )
 }
 
 function buildTemplate(ctx) {
-  return pipe('./src/template.html', [
+  return pipe(
+    './src/template.html',
     $.preprocess({context: ctx}),
-    html2js('const TEMPLATE = \'$$\'')
-  ], './tmp')
+    html2js('const TEMPLATE = \'$$\''),
+    './tmp'
+  )
 }
diff --git a/src/config/chrome/background.js b/src/config/chrome/background.js
index f1497dd..ef0b5e2 100644
--- a/src/config/chrome/background.js
+++ b/src/config/chrome/background.js
@@ -1,20 +1,20 @@
-chrome.tabs.onUpdated.addListener(function(tabId, changeInfo, tab) {
+chrome.tabs.onUpdated.addListener((tabId, changeInfo, tab) => {
   if (changeInfo.status !== 'loading') return
 
   chrome.tabs.executeScript(tabId, {
-    code  : 'var injected = window.octotreeInjected; window.octotreeInjected = true; injected;',
-    runAt : 'document_start'
-  }, function(res) {
+    code: 'var injected = window.octotreeInjected; window.octotreeInjected = true; injected;',
+    runAt: 'document_start'
+  }, (res) => {
     if (chrome.runtime.lastError || // don't continue if error (i.e. page isn't in permission list)
         res[0]) // value of `injected` above: don't inject twice
       return
 
-    var cssFiles = [
+    const cssFiles = [
       'jstree.css',
       'octotree.css'
     ]
 
-    var jsFiles = [
+    const jsFiles = [
       'jquery.js',
       'jquery-ui.js',
       'jquery.pjax.js',
@@ -24,28 +24,24 @@ chrome.tabs.onUpdated.addListener(function(tabId, changeInfo, tab) {
     ]
 
     eachTask([
-      function(cb) {
-        eachItem(cssFiles, inject('insertCSS'), cb)
-      },
-      function(cb) {
-        eachItem(jsFiles, inject('executeScript'), cb)
-      }
+      (cb) => eachItem(cssFiles, inject('insertCSS'), cb),
+      (cb) => eachItem(jsFiles, inject('executeScript'), cb)
     ])
 
     function inject(fn) {
-      return function(file, cb) {
+      return (file, cb) => {
         chrome.tabs[fn](tabId, { file: file, runAt: 'document_start' }, cb)
       }
     }
   })
 })
 
-chrome.runtime.onMessage.addListener(function(req, sender, sendRes) {
-  var handler = {
-    requestPermissions: function() {
-      var urls = (req.urls || [])
-        .filter(function(url) { return url.trim() !== '' })
-        .map(function(url) {
+chrome.runtime.onMessage.addListener((req, sender, sendRes) => {
+  const handler = {
+    requestPermissions: () => {
+      const urls = (req.urls || [])
+        .filter((url) => url.trim() !== '')
+        .map((url) => {
           if (url.slice(-2) === '/*') return url
           if (url.slice(-1) === '/') return url + '*'
           return url + '/*'
@@ -56,7 +52,7 @@ chrome.runtime.onMessage.addListener(function(req, sender, sendRes) {
         removeUnnecessaryPermissions()
       }
       else {
-        chrome.permissions.request({ origins: urls }, function(granted) {
+        chrome.permissions.request({ origins: urls }, (granted) => {
           sendRes(granted)
           removeUnnecessaryPermissions()
         })
@@ -64,11 +60,18 @@ chrome.runtime.onMessage.addListener(function(req, sender, sendRes) {
       return true
 
       function removeUnnecessaryPermissions() {
-        chrome.permissions.getAll(function(permissions) {
-          var toBeRemovedUrls = permissions.origins.filter(function(url) {
-            return (url !== 'https://github.com/*' || url !== 'https://gitlab.com/*') && !~urls.indexOf(url)
+        const whitelist = urls.concat([
+          'https://github.com/*',
+          'https://gitlab.com/*'
+        ])
+        chrome.permissions.getAll((permissions) => {
+          const toBeRemovedUrls = permissions.origins.filter((url) => {
+            return !~whitelist.indexOf(url)
           })
-          if (toBeRemovedUrls.length) chrome.permissions.remove({ origins: toBeRemovedUrls })
+
+          if (toBeRemovedUrls.length) {
+            chrome.permissions.remove({ origins: toBeRemovedUrls })
+          }
         })
       }
     }
@@ -78,18 +81,15 @@ chrome.runtime.onMessage.addListener(function(req, sender, sendRes) {
 })
 
 function eachTask(tasks, done) {
-  next(0)
-  function next(index) {
+  (function next(index = 0) {
     if (index === tasks.length) done && done()
-    else tasks[index](function() { next(index + 1) })
-  }
+    else tasks[index](() => next(++index))
+  })()
 }
 
 function eachItem(arr, iter, done) {
-  var tasks = arr.map(function(item) {
-    return function(next) {
-      iter(item, next)
-    }
+  const tasks = arr.map((item) => {
+    return (cb) => iter(item, cb)
   })
   return eachTask(tasks, done)
-}
\ No newline at end of file
+}
diff --git a/src/config/firefox/firefox.js b/src/config/firefox/firefox.js
index a2944d6..30ddf05 100644
--- a/src/config/firefox/firefox.js
+++ b/src/config/firefox/firefox.js
@@ -1,5 +1,5 @@
-var data = require('sdk/self').data
-  , pageMod = require('sdk/page-mod')
+const data = require('sdk/self').data
+const pageMod = require('sdk/page-mod')
 
 pageMod.PageMod({
   include: ['https://github.com/*', 'https://gitlab.com/*'],