purge polyfill from firefox branch; fix 'lookup doesn't work on certain strings when certain json dictionaries are loaded' bug

reader.html

@@ -73,7 +73,6 @@ body > p:nth-of-type(1)
     bottom: calc( 10px + 2em );
 }
 </style>
-<script src="include/browser-polyfill.min.js" charset="UTF-8"></script>
 <script src="reader.js" charset="UTF-8"></script>
 <script src="texthook.js" charset="UTF-8"></script>
 </head>