diff --git a/core/modules/simpletest/src/BrowserTestBase.php b/core/modules/simpletest/src/BrowserTestBase.php
index 0fe90f1..e917829 100644
--- a/core/modules/simpletest/src/BrowserTestBase.php
+++ b/core/modules/simpletest/src/BrowserTestBase.php
@@ -248,10 +248,14 @@ protected function initMink() {
     $this->mink->setDefaultSessionName('default');
     $this->registerSessions();
 
-    // Fire up the first request to the front page in order to be able to  set
-    // a cookie later.
-    // @fixme This is done to circumvent:
-    // WebDriver\Exception\UnableToSetCookie: {"errorMessage":"Unable to set Cookie: no URL has been loaded yet","request":{"headers":{"Accept":"application/json;charset=UTF-8","Content-Length":"164","Content-Type":"application/json;charset=UTF-8","Host":"127.0.0.1:8910"},"httpVersion":"1.1","method":"POST","post":"{\"cookie\":{\"name\":\"SIMPLETEST_USER_AGENT\",\"value\":\"simpletest472558;1441488302;55eb5dae78eeb7.36607058;IxhRvB7dhbDAMurfBshqgUwEOpAPPKybnJMv0JgaG8Q\",\"secure\":false}}","url":"/cookie","urlParsed":{"anchor":"","query":"","file":"cookie","directory":"/","path":"/cookie","relative":"/cookie","port":"","host":"","password":"","user":"","userInfo":"","authority":"","protocol":"","source":"/cookie","queryKey":{},"chunks":["cookie"]},"urlOriginal":"/session/91aef6b0-5414-11e5-9028-67c7fcbbdc3b/cookie"}}
+    // According to the W3C WebDriver specification a cookie can only be set if
+    // the cookie domain is equal to the domain of the active document. When the
+    // browser starts up the active document is not our domain but 'about:blank'
+    // or similar. To be able to set our User-Agent and Xdebug cookies at the
+    // start of the test we now do a request to the front page so the active
+    // document matches the domain.
+    // @see https://w3c.github.io/webdriver/webdriver-spec.html#add-cookie
+    // @see https://www.w3.org/Bugs/Public/show_bug.cgi?id=20975
     $session = $this->getSession();
     $session->visit($this->baseUrl);
 
diff --git a/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php b/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
index 81d8425..188cd7e 100644
--- a/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
+++ b/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
@@ -5,7 +5,7 @@
 use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
 
 /**
- * Tests a browser with javascript.
+ * Tests if we can execute JavaScript in the browser.
  *
  * @group javascript
  */
@@ -16,7 +16,6 @@ public function testJavascript() {
     $session = $this->getSession();
 
     $session->resizeWindow(400, 300);
-    $session->wait(1000, 'false');
     $javascript = <<<JS
     (function(){
         var w = window,
@@ -24,16 +23,12 @@ public function testJavascript() {
         e = d.documentElement,
         g = d.getElementsByTagName('body')[0],
         x = w.innerWidth || e.clientWidth || g.clientWidth,
-        y = w.innerHeight|| e.clientHeight|| g.clientHeight;
-        var size = {};
-        size["width"]=x;
-        size["height"]= y;
-        return size;
+        y = w.innerHeight || e.clientHeight|| g.clientHeight;
+        return x == 400 && y == 300;
     }());
 JS;
-    $pageSize = $session->evaluateScript($javascript);
-    $this->assertEquals(400, $pageSize["width"]);
-    $this->assertEquals(300, $pageSize["height"]);
+    $result = $session->wait(1000, $javascript);
+    $this->assertTrue($result);
   }
 
 }
diff --git a/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php b/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
index 8428643..c22443c 100644
--- a/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
+++ b/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
@@ -5,7 +5,7 @@
 use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
 
 /**
- * Basic toolbar testing.
+ * Tests the JavaScript functionality of the toolbar.
  *
  * @group toolbar
  */
@@ -16,6 +16,9 @@ class ToolbarIntegrationTest extends JavascriptTestBase {
    */
   public static $modules = ['toolbar', 'node'];
 
+  /**
+   * Tests if the toolbar can be toggled with JavaScript.
+   */
   public function testToolbarToggling() {
     $admin_user = $this->drupalCreateUser([
       'access toolbar',
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
index e95fa49..00daa43 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
@@ -3,14 +3,12 @@
 namespace Drupal\FunctionalJavascriptTests;
 
 use Drupal\simpletest\BrowserTestBase;
-use GuzzleHttp\Exception\ConnectException;
 use Zumba\Mink\Driver\PhantomJSDriver;
 
 /**
- * Runs a browser test using phantomJS.
+ * Runs a browser test using PhantomJS.
  *
- * Use this test baseclass if you want to test expected behaviour of some
- * JavaScript.
+ * Base class for testing browser interaction implemented in JavaScript.
  */
 abstract class JavascriptTestBase extends BrowserTestBase {
 
@@ -23,7 +21,7 @@
    * {@inheritdoc}
    */
   protected function initMink() {
-    // Setup some template cache using by the phantomjs mink driver.
+    // Set up the template cache used by the PhantomJS mink driver.
     $path = $this->tempFilesDirectory . DIRECTORY_SEPARATOR . 'browsertestbase-templatecache';
     $this->minkDefaultDriverArgs = [
       'http://127.0.0.1:8510',
diff --git a/core/tests/README.md b/core/tests/README.md
index df091f3..dfd1154 100644
--- a/core/tests/README.md
+++ b/core/tests/README.md
@@ -1,14 +1,15 @@
 # Running tests
 
-## Function tests
+## Functional tests
 
-* Start phantomjs:
-```
-phantomjs --ssl-protocol=any --ignore-ssl-errors=true vendor/jcalderonzumba/gastonjs/src/Client/main.js 8510 1024 768 2>&1 >> /dev/null &
-```
-* Run the function tests:
-```
-export SIMPLETEST_DB='mysql://root@localhost/dev_d8'
-export SIMPLETEST_BASE_URL='http://d8.dev'
-vendor/bin/phpunit -c core core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
-```
+* Start PhantomJS:
+  ```
+  phantomjs --ssl-protocol=any --ignore-ssl-errors=true ./vendor/jcalderonzumba/gastonjs/src/Client/main.js 8510 1024 768 2>&1 >> /dev/null &
+  ```
+* Run the functional tests:
+  ```
+  export SIMPLETEST_DB='mysql://root@localhost/dev_d8'
+  export SIMPLETEST_BASE_URL='http://d8.dev'
+  ./vendor/bin/phpunit -c core --testsuite functional
+  ./vendor/bin/phpunit -c core --testsuite functional-javascript
+  ```