Check for shared worker support before enabling them

boards/static/js/form.js

@@ -85,7 +85,7 b' function selectFileChoice() {'
 
 $(document).ready(function() {
     var powDifficulty = parseInt($('body').attr('data-pow-difficulty'));
-    if (powDifficulty > 0) {
+    if (powDifficulty > 0 && typeof SharedWorker != 'undefined') {
         var worker = new SharedWorker($('#powScript').attr('src'));
         worker.port.onmessage = function(e) {
             var form = $('#form');

boards/static/js/main.js

@@ -83,7 +83,7 b' function updateFavPosts(data) {'
 
 function initFavPanel() {
     var favPanelButton = $('#fav-panel-btn');
-    if (favPanelButton.length > 0) {
+    if (favPanelButton.length > 0 && typeof SharedWorker != 'undefined') {
         var worker = new SharedWorker($('body').attr('data-update-script'));
         worker.port.onmessage = function(e) {
             updateFavPosts(e.data);