diff --git a/gulp/.babelrc b/gulp/.babelrc
new file mode 100644
index 00000000..a0765e18
--- /dev/null
+++ b/gulp/.babelrc
@@ -0,0 +1,3 @@
+{
+    "presets": ["es2015"]
+}
diff --git a/gulp/babel-es6.config.js b/gulp/babel-es6.config.js
index e687f070..b3f088f9 100644
--- a/gulp/babel-es6.config.js
+++ b/gulp/babel-es6.config.js
@@ -10,7 +10,6 @@ module.exports = function (api) {
                 loose: true,
                 spec: false,
                 modules: "auto",
-                // debug: true
             },
         ],
     ];
diff --git a/gulp/babel.config.js b/gulp/babel.config.js
index 0552a94b..44d47d17 100644
--- a/gulp/babel.config.js
+++ b/gulp/babel.config.js
@@ -4,18 +4,24 @@ module.exports = function (api) {
         [
             "@babel/preset-env",
             {
-                targets: "android >= 4.4.4",
+                targets: "cover 99.5%",
                 useBuiltIns: "usage",
                 corejs: 3,
                 loose: true,
                 spec: false,
                 modules: "auto",
-                // debug: true
             },
         ],
     ];
     const plugins = [
         "closure-elimination",
+        // var is faster than let and const!
+        [
+            "@babel/plugin-transform-block-scoping",
+            {
+                throwIfClosureRequired: false,
+            },
+        ],
         [
             "@babel/plugin-transform-classes",
             {
diff --git a/gulp/webpack.production.config.js b/gulp/webpack.production.config.js
index e06e15c1..fab5dbeb 100644
--- a/gulp/webpack.production.config.js
+++ b/gulp/webpack.production.config.js
@@ -61,7 +61,8 @@ module.exports = ({
             // Display bailout reasons
             optimizationBailout: true,
         },
-        devtool: "source-map",
+        // devtool: "source-map",
+        devtool: false,
         resolve: {
             alias: {
                 "global-compression": path.resolve(__dirname, "..", "src", "js", "core", "lzstring.js"),
@@ -85,7 +86,7 @@ module.exports = ({
             minimizer: [
                 new TerserPlugin({
                     parallel: true,
-                    sourceMap: true,
+                    sourceMap: false,
                     cache: false,
                     terserOptions: {
                         ecma: es6 ? 6 : 5,
@@ -178,6 +179,10 @@ module.exports = ({
                 patterns: ["../src/js/**/*.js"],
             }),
 
+            // new webpack.SourceMapDevToolPlugin({
+            //     filename: "[name].map",
+            //     publicPath: "/v/" + utils.getRevision() + "/",
+            // }),
             // new ReplaceCompressBlocks()
             // new webpack.optimize.ModuleConcatenationPlugin()
             // new WebpackDeepScopeAnalysisPlugin()
@@ -242,13 +247,23 @@ module.exports = ({
                 },
                 {
                     test: /\.worker\.js$/,
-                    use: {
-                        loader: "worker-loader",
-                        options: {
-                            fallback: false,
-                            inline: true,
+                    use: [
+                        {
+                            loader: "worker-loader",
+                            options: {
+                                fallback: false,
+                                inline: true,
+                            },
                         },
-                    },
+                        {
+                            loader: "babel-loader?cacheDirectory",
+                            options: {
+                                configFile: require.resolve(
+                                    es6 ? "./babel-es6.config.js" : "./babel.config.js"
+                                ),
+                            },
+                        },
+                    ],
                 },
                 {
                     test: /\.md$/,
diff --git a/src/js/webworkers/background_animation_frame_emittter.worker.js b/src/js/webworkers/background_animation_frame_emittter.worker.js
index 5a3fe5c9..c927b2d3 100644
--- a/src/js/webworkers/background_animation_frame_emittter.worker.js
+++ b/src/js/webworkers/background_animation_frame_emittter.worker.js
@@ -1,12 +1,12 @@
 // We clamp high deltas so 30 fps is fairly ok
-const bgFps = 30;
-const desiredMsDelay = 1000 / bgFps;
+var bgFps = 30;
+var desiredMsDelay = 1000 / bgFps;
 
 let lastTick = 0;
 
 function tick() {
-    const now = performance.now();
-    const delta = now - lastTick;
+    var now = performance.now();
+    var delta = now - lastTick;
     lastTick = now;
 
     // @ts-ignore