adding gecko polyfill

ext/bg/background.html

@@ -4,6 +4,7 @@
     <script src="../lib/handlebars.min.js"></script>
     <script src="../lib/dexie.min.js"></script>
     <script src="../lib/wanakana.min.js"></script>
+    <script src="js/gecko.js"></script>
     <script src="js/ankiconnect.js"></script>
     <script src="js/ankinull.js"></script>
     <script src="js/templates.js"></script>

ext/bg/js/gecko.js

@@ -0,0 +1,18 @@
+console.log('blah');
+
+//
+// Gecko does not currently support chrome.storage.sync, use storage.local instead
+// https://bugzilla.mozilla.org/show_bug.cgi?id=1220494
+if (!chrome.storage.sync) {
+    chrome.storage.sync = chrome.storage.local;
+}
+
+// Gecko does not currently support chrome.runtime.onInstalled, just ignore calls to it
+// (https://bugzilla.mozilla.org/show_bug.cgi?id=1252871)
+if (!chrome.runtime.onInstalled) {
+    chrome.runtime.onInstalled = {
+        'addListener' : function(){},
+        'hasListener' : function(){},
+        'removeListener' : function(){}
+    };
+}

ext/bg/options.html

@@ -232,6 +232,7 @@
         <script src="../lib/bootstrap-3.3.6-dist/js/bootstrap.min.js"></script>
         <script src="../lib/handlebars.min.js"></script>
         <script src="js/templates.js"></script>
+        <script src="js/gecko.js"></script>
         <script src="js/options.js"></script>
         <script src="js/options-form.js"></script>
     </body>