Bug 993137 - Make color picker popup test less fragile. r=mounir

dom/html/test/forms/test_input_color_picker_popup.html

@@ -9,6 +9,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
   <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
   <script type="application/javascript" src="/tests/SimpleTest/EventUtils.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <style> label { display: block } </style>
   <script type="application/javascript;version=1.8">
 
   /** Test the behaviour of the <input type='color'> when clicking on it from