propagate FIREFOX_EXTENSION_NEEDED event

JitsiConference.js

 var XMPPEvents = require("./service/xmpp/XMPPEvents");
 var AuthenticationEvents = require("./service/authentication/AuthenticationEvents");
 var RTCEvents = require("./service/RTC/RTCEvents");
+var DSEvents = require("../../service/desktopsharing/DesktopSharingEventTypes");
 var EventEmitter = require("events");
 var JitsiConferenceEvents = require("./JitsiConferenceEvents");
 var JitsiConferenceErrors = require("./JitsiConferenceErrors");
         conference.eventEmitter.emit(JitsiConferenceEvents.MESSAGE_RECEIVED, id, txt, ts);
     });
 
+    conference.rtc.addListener(DSEvents.FIREFOX_EXTENSION_NEEDED, function (url) {
+        conference.eventEmitter.emit(JitsiConferenceEvents.FIREFOX_EXTENSION_NEEDED, url);
+    });
+
     conference.rtc.addListener(RTCEvents.DOMINANTSPEAKER_CHANGED, function (id) {
         if(conference.lastDominantSpeaker !== id && conference.room) {
             conference.lastDominantSpeaker = id;

JitsiConferenceEvents.js

     /**
      * Indicates that phone number changed.
      */
-    PHONE_NUMBER_CHANGED: "conference.phoneNumberChanged"
+    PHONE_NUMBER_CHANGED: "conference.phoneNumberChanged",
+    /**
+     * Indicates that to proceed with screen sharing
+     * browser extension must be installed first.
+     */
+    FIREFOX_EXTENSION_NEEDED: "conference.firefoxExtensionRequired"
 };
 
 module.exports = JitsiConferenceEvents;

doc/API.md

         - KICKED - notifies that user has been kicked from the conference.
         - START_MUTED_POLICY_CHANGED - notifies that all new participants will join with muted audio/video stream (parameters - JS object with 2 properties - audio(boolean), video(boolean))
         - STARTED_MUTED - notifies that the local user has started muted
+        - FIREFOX_EXTENSION_NEEDED - notifies that browser extension must be installed to proceed with screen sharing (parameters - extension url(string))
 
     2. connection
         - CONNECTION_FAILED - indicates that the server connection failed.

modules/RTC/RTC.js

 var JitsiLocalTrack = require("./JitsiLocalTrack.js");
 var DataChannels = require("./DataChannels");
 var JitsiRemoteTrack = require("./JitsiRemoteTrack.js");
-var DesktopSharingEventTypes
-    = require("../../service/desktopsharing/DesktopSharingEventTypes");
 var MediaStreamType = require("../../service/RTC/MediaStreamTypes");
 var RTCEvents = require("../../service/RTC/RTCEvents.js");