Firefox: add basic blocking + some fixes

platform/firefox/vapi-client.js

@@ -84,7 +84,6 @@ vAPI.messaging = {
     listeners: {},
     requestId: 1,
     connectorId: uniqueId(),
-    bgMessageName: 'µBlock:background',
 
     setup: function() {
         this.connector = function(msg) {
@@ -125,7 +124,7 @@ vAPI.messaging = {
                     vAPI.messaging.listeners[message.requestId] = callback;
                 }
 
-                sendAsyncMessage(vAPI.messaging.bgMessageName, message);
+                sendAsyncMessage('ublock:background', message);
             },
             close: function() {
                 delete vAPI.messaging.channels[this.portName];