Adds config property for enabling firefox support

app.js

     if (RTC === null) {
         window.location.href = 'webrtcrequired.html';
         return;
+    } else if (RTC.browser !== 'chrome' &&
+        config.enableFirefoxSupport !== true) {
+        window.location.href = 'chromeonly.html';
+        return;
     }
 
     obtainAudioAndVideoPermissions(function (stream) {

config.js

     useBundle: true,
     enableRecording: false,
     enableWelcomePage: true,
-    enableSimulcast: false
+    enableSimulcast: false,
+    enableFirefoxSupport: false //firefox support is still experimental, only one-to-one conferences with chrome focus
+    // will work when simulcast, bundle, mux, lastN and SCTP are disabled.
 };

libs/colibri/colibri.focus.js

         'a=rtcp-fb:100 ccm fir\r\n' +
         'a=rtcp-fb:100 nack\r\n' +
         'a=rtcp-fb:100 nack pli\r\n' +
-//        'a=rtcp-fb:100 goog-remb\r\n' +
+            (config.enableFirefoxSupport? "" : 'a=rtcp-fb:100 goog-remb\r\n') +
         'a=rtpmap:116 red/90000\r\n' +
         'a=rtpmap:117 ulpfec/90000\r\n' +
         (config.useRtcpMux ? 'a=rtcp-mux\r\n' : '') +