diff --git a/.eslintignore b/.eslintignore
index bc3e05a12..d8de39a3e 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -8,6 +8,8 @@ external/webL10n/
 external/cmapscompress/
 external/builder/fixtures/
 external/builder/fixtures_esprima/
+src/shared/cffStandardStrings.js
+src/shared/fonts_utils.js
 test/tmp/
 test/features/
 test/pdfs/
diff --git a/.eslintrc b/.eslintrc
index 9fecb95ea..9040d7789 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -1,6 +1,7 @@
 {
   "parserOptions": {
-    "ecmaVersion": 5,
+    "ecmaVersion": 6,
+    "sourceType": "module"
   },
 
   "env": {
@@ -78,7 +79,7 @@
     }],
 
     // Strict Mode
-    "strict": ["error", "global"],
+    "strict": ["off", "global"],
 
     // Variables
     "no-catch-shadow": "error",
diff --git a/extensions/chromium/.eslintrc b/extensions/chromium/.eslintrc
new file mode 100644
index 000000000..c3e462548
--- /dev/null
+++ b/extensions/chromium/.eslintrc
@@ -0,0 +1,9 @@
+{
+  "extends": [
+    ../../.eslintrc
+  ],
+
+  "parserOptions": {
+    "sourceType": "script"
+  },
+}
diff --git a/extensions/firefox/.eslintrc b/extensions/firefox/.eslintrc
index 89561cf5f..9f7c5e5f1 100644
--- a/extensions/firefox/.eslintrc
+++ b/extensions/firefox/.eslintrc
@@ -4,7 +4,8 @@
   ],
 
   "parserOptions": {
-    "ecmaVersion": 6
+    "ecmaVersion": 6,
+    "sourceType": "script"
   },
 
   "rules": {
diff --git a/external/builder/preprocessor2.js b/external/builder/preprocessor2.js
index bf22ac64d..b2142cb65 100644
--- a/external/builder/preprocessor2.js
+++ b/external/builder/preprocessor2.js
@@ -1,6 +1,6 @@
 'use strict';
 
-var esprima = require('esprima');
+var acorn = require('acorn');
 var escodegen = require('escodegen');
 var vm = require('vm');
 var fs = require('fs');
@@ -49,7 +49,7 @@ function handlePreprocessorAction(ctx, actionName, args, loc) {
           return {type: 'Literal', value: result, loc: loc};
         }
         if (typeof result === 'object') {
-          var parsedObj = esprima.parse('(' + JSON.stringify(result) + ')');
+          var parsedObj = acorn.parse('(' + JSON.stringify(result) + ')');
           parsedObj.body[0].expression.loc = loc;
           return parsedObj.body[0].expression;
         }
@@ -66,7 +66,7 @@ function handlePreprocessorAction(ctx, actionName, args, loc) {
                                jsonPath.substring(ROOT_PREFIX.length));
         }
         var jsonContent = fs.readFileSync(jsonPath).toString();
-        var parsedJSON = esprima.parse('(' + jsonContent + ')');
+        var parsedJSON = acorn.parse('(' + jsonContent + ')');
         parsedJSON.body[0].expression.loc = loc;
         return parsedJSON.body[0].expression;
     }
@@ -354,16 +354,21 @@ function preprocessPDFJSCode(ctx, code) {
       adjustMultilineComment: saveComments,
     }
   };
+  var comments;
   var parseComment = {
-    loc: true,
-    attachComment: saveComments
+    locations: true,
+    onComments: saveComments || (comments = []),
+    sourceType: 'module',
   };
   var codegenOptions = {
     format: format,
     comment: saveComments,
-    parse: esprima.parse
+    parse: acorn.parse,
   };
-  var syntax = esprima.parse(code, parseComment);
+  var syntax = acorn.parse(code, parseComment);
+  if (saveComments) {
+    escodegen.attachComments(syntax, comments);
+  }
   traverseTree(ctx, syntax);
   return escodegen.generate(syntax, codegenOptions);
 }
diff --git a/gulpfile.js b/gulpfile.js
index c40378052..fe9fdfe49 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -109,6 +109,12 @@ function createWebpackConfig(defines, output) {
     },
     module: {
       loaders: [
+        {
+          loader: 'babel-loader',
+          options: {
+            plugins: ['transform-es2015-modules-commonjs']
+          }
+        },
         {
           loader: path.join(__dirname, 'external/webpack/pdfjsdev-loader.js'),
           options: {
@@ -116,7 +122,7 @@ function createWebpackConfig(defines, output) {
             saveComments: false,
             defines: bundleDefines
           }
-        }
+        },
       ]
     }
   };
@@ -928,6 +934,10 @@ gulp.task('jsdoc', function (done) {
 gulp.task('lib', ['buildnumber'], function () {
   function preprocess(content) {
     content = preprocessor2.preprocessPDFJSCode(ctx, content);
+    content = babel.transform(content, {
+      sourceType: 'module',
+      plugins: ['transform-es2015-modules-commonjs'],
+    }).code;
     var removeCjsSrc =
       /^(var\s+\w+\s*=\s*require\('.*?)(?:\/src)(\/[^']*'\);)$/gm;
     content = content.replace(removeCjsSrc, function (all, prefix, suffix) {
@@ -935,6 +945,7 @@ gulp.task('lib', ['buildnumber'], function () {
     });
     return licenseHeader + content;
   }
+  var babel = require('babel-core');
   var versionInfo = getVersionJSON();
   var ctx = {
     rootPath: __dirname,
diff --git a/make.js b/make.js
index 19e7e3c93..5dd9203bc 100644
--- a/make.js
+++ b/make.js
@@ -19,9 +19,8 @@
 try {
   require('shelljs/make');
 } catch (e) {
-  console.log('ShellJS is not installed. Run "npm install" to install ' +
-              'all dependencies.');
-  return;
+  throw new Error('ShellJS is not installed. Run "npm install" to install ' +
+                  'all dependencies.');
 }
 
 var fs = require('fs');
diff --git a/package.json b/package.json
index 262e4788e..190d398e4 100644
--- a/package.json
+++ b/package.json
@@ -2,9 +2,12 @@
   "name": "pdf.js",
   "version": "0.8.0",
   "devDependencies": {
+    "acorn": "^4.0.11",
+    "babel-core": "^6.23.1",
+    "babel-loader": "^6.4.0",
+    "babel-plugin-transform-es2015-modules-commonjs": "^6.23.0",
     "escodegen": "^1.8.0",
     "eslint": "^3.11.1",
-    "esprima": "^2.7.2",
     "gulp": "^3.9.1",
     "gulp-rename": "^1.2.2",
     "gulp-replace": "^0.5.4",
@@ -22,6 +25,7 @@
     "shelljs": "~0.4.0",
     "streamqueue": "^1.1.1",
     "systemjs": "^0.20.7",
+    "systemjs-plugin-babel": "0.0.21",
     "typogr": "~0.6.5",
     "uglify-js": "^2.6.1",
     "webpack": "^2.2.1",
diff --git a/systemjs.config.js b/systemjs.config.js
index 83a128ac1..f34a2c146 100644
--- a/systemjs.config.js
+++ b/systemjs.config.js
@@ -29,10 +29,13 @@
     throw new Error('Cannot configure SystemJS');
   }
 
+  var PluginBabelPath = 'node_modules/systemjs-plugin-babel/plugin-babel.js';
+  var SystemJSPluginBabelPath =
+    'node_modules/systemjs-plugin-babel/systemjs-babel-browser.js';
+
   SystemJS.config({
     packages: {
       '': {
-        format: 'amd',
         defaultExtension: 'js',
       }
     },
@@ -40,6 +43,18 @@
       'pdfjs': new URL('src', baseLocation).href,
       'pdfjs-web': new URL('web', baseLocation).href,
       'pdfjs-test': new URL('test', baseLocation).href,
-    }
+    },
+    meta: {
+      '*': {
+        scriptLoad: false,
+        esModule: true
+      }
+    },
+    map: {
+      'plugin-babel': new URL(PluginBabelPath, baseLocation).href,
+      'systemjs-babel-build':
+        new URL(SystemJSPluginBabelPath, baseLocation).href,
+    },
+    transpiler: 'plugin-babel'
   });
 })();
diff --git a/web/debugger.js b/web/debugger.js
index 4aee67fc5..d3b454e5b 100644
--- a/web/debugger.js
+++ b/web/debugger.js
@@ -502,7 +502,7 @@ var Stats = (function Stats() {
 })();
 
 // Manages all the debugging tools.
-var PDFBug = (function PDFBugClosure() {
+window.PDFBug = (function PDFBugClosure() {
   var panelWidth = 300;
   var buttons = [];
   var activePanel = null;