diff --git a/karma.conf.js b/karma.conf.js
index a455a9c9..5cbd7a5d 100644
--- a/karma.conf.js
+++ b/karma.conf.js
@@ -4,7 +4,6 @@ module.exports = (config) => {
   const customLaunchers = {};
   let browsers = [];
   let useSauce = false;
-  let transpileToES5 = ['internet explorer'].includes(process.env.TEST_BROWSER_NAME);
 
   // use Sauce when running on Travis
   if (process.env.TRAVIS_JOB_NUMBER) {
@@ -53,7 +52,7 @@ module.exports = (config) => {
 
     // frameworks to use
     // available frameworks: https://npmjs.org/browse/keyword/karma-adapter
-    frameworks: ['requirejs', 'mocha', 'sinon-chai'],
+    frameworks: ['mocha', 'sinon-chai'],
 
     // list of files / patterns to load in the browser (loaded in order)
     files: [
@@ -61,9 +60,11 @@ module.exports = (config) => {
       { pattern: 'app/webutil.js', included: false },
       { pattern: 'core/**/*.js', included: false },
       { pattern: 'vendor/pako/**/*.js', included: false },
+      { pattern: 'vendor/browser-es-module-loader/dist/*.js*', included: false },
       { pattern: 'tests/test.*.js', included: false },
       { pattern: 'tests/fake.*.js', included: false },
       { pattern: 'tests/assertions.js', included: false },
+      'vendor/promise.js',
       'tests/karma-test-main.js',
     ],
 
@@ -85,26 +86,6 @@ module.exports = (config) => {
     // available browser launchers: https://npmjs.org/browse/keyword/karma-launcher
     browsers: browsers,
 
-    // preprocess matching files before serving them to the browser
-    // available preprocessors: https://npmjs.org/browse/keyword/karma-preprocessor
-    preprocessors: {
-      'app/localization.js': ['babel'],
-      'app/webutil.js': ['babel'],
-      'core/**/*.js': ['babel'],
-      'tests/test.*.js': ['babel'],
-      'tests/fake.*.js': ['babel'],
-      'tests/assertions.js': ['babel'],
-      'vendor/pako/**/*.js': ['babel'],
-    },
-
-    babelPreprocessor: {
-      options: {
-        presets: transpileToES5 ? ['es2015'] : [],
-        plugins: ['transform-es2015-modules-amd', 'syntax-dynamic-import'],
-        sourceMap: 'inline',
-      },
-    },
-
     // test results reporter to use
     // possible values: 'dots', 'progress'
     // available reporters: https://npmjs.org/browse/keyword/karma-reporter
diff --git a/package.json b/package.json
index 7394a20b..24cb763f 100644
--- a/package.json
+++ b/package.json
@@ -46,10 +46,8 @@
     "fs-extra": "^1.0.0",
     "jsdom": "*",
     "karma": "^1.3.0",
-    "karma-babel-preprocessor": "^6.0.1",
     "karma-mocha": "^1.3.0",
     "karma-mocha-reporter": "^2.2.0",
-    "karma-requirejs": "^1.1.0",
     "karma-sauce-launcher": "^1.0.0",
     "karma-sinon-chai": "^2.0.0",
     "mocha": "^3.1.2",
diff --git a/tests/karma-test-main.js b/tests/karma-test-main.js
index 334b771c..c1b3ad4b 100644
--- a/tests/karma-test-main.js
+++ b/tests/karma-test-main.js
@@ -9,8 +9,39 @@ Object.keys(window.__karma__.files).forEach(function (file) {
     }
 });
 
-require.config({
-    baseUrl: '/base',
-    deps: allTestFiles.concat(extraFiles),
-    callback: window.__karma__.start,
+// Stub out mocha's start function so we can run it once we're done loading
+mocha.origRun = mocha.run;
+mocha.run = function () {};
+
+let script;
+
+// Script to import all our tests
+script = document.createElement("script");
+script.type = "module";
+script.text = "";
+let allModules = allTestFiles.concat(extraFiles);
+allModules.forEach(function (file) {
+    script.text += "import \"" + file + "\";\n";
 });
+script.text += "\nmocha.origRun();\n";
+document.body.appendChild(script);
+
+// Fallback code for browsers that don't support modules (IE)
+script = document.createElement("script");
+script.type = "module";
+script.text = "window._noVNC_has_module_support = true;\n";
+document.body.appendChild(script);
+
+function fallback() {
+    if (!window._noVNC_has_module_support) {
+        /* eslint-disable no-console */
+        if (console)
+            console.log("No module support detected. Loading fallback...");
+        /* eslint-enable no-console */
+        let loader = document.createElement("script");
+        loader.src = "base/vendor/browser-es-module-loader/dist/browser-es-module-loader.js";
+        document.body.appendChild(loader);
+    }
+}
+
+setTimeout(fallback, 500);