fix(conference) avoid double prompts in Firefox after choosing non-default device.

* fix(conference) avoid double prompts in Firefox after choosing non-default device

* addressed linting errors

conference.js

 
         APP.store.dispatch(updateDeviceList(devices));
 
+        // Firefox users can choose their preferred device in the gUM prompt. In that case
+        // we should respect that and not attempt to switch to the preferred device from
+        // our settings.
+        const newLabelsOnly = mediaDeviceHelper.newDeviceListAddedLabelsOnly(oldDevices, devices);
         const newDevices
             = mediaDeviceHelper.getNewMediaDevicesAfterDeviceListChanged(
                 devices,
                 this.isSharingScreen,
                 localVideo,
-                localAudio);
+                localAudio,
+                newLabelsOnly);
         const promises = [];
         const audioWasMuted = this.isLocalAudioMuted();
         const videoWasMuted = this.isLocalVideoMuted();

modules/devices/mediaDeviceHelper.js

  * list of available devices has been changed.
  * @param {MediaDeviceInfo[]} newDevices
  * @param {JitsiLocalTrack} localAudio
+ * @param {boolean} newLabel
  * @returns {string|undefined} - ID of new microphone device to use, undefined
  *      if audio input device should not be changed.
  */
-function getNewAudioInputDevice(newDevices, localAudio) {
+function getNewAudioInputDevice(newDevices, localAudio, newLabel) {
     const availableAudioInputDevices = newDevices.filter(
         d => d.kind === 'audioinput');
     const selectedAudioInputDeviceId = getUserSelectedMicDeviceId(APP.store.getState());
             return availableAudioInputDevices[0].deviceId;
         }
     } else if (selectedAudioInputDevice
-        && selectedAudioInputDeviceId !== localAudio.getDeviceId()) {
+        && selectedAudioInputDeviceId !== localAudio.getDeviceId()
+        && !newLabel) {
 
         // And here we handle case when we already have some device working,
         // but we plug-in a "preferred" (previously selected in settings, stored
  * list of available devices has been changed.
  * @param {MediaDeviceInfo[]} newDevices
  * @param {JitsiLocalTrack} localVideo
+ * @param {boolean} newLabel
  * @returns {string|undefined} - ID of new camera device to use, undefined
  *      if video input device should not be changed.
  */
-function getNewVideoInputDevice(newDevices, localVideo) {
+function getNewVideoInputDevice(newDevices, localVideo, newLabel) {
     const availableVideoInputDevices = newDevices.filter(
         d => d.kind === 'videoinput');
     const selectedVideoInputDeviceId = getUserSelectedCameraDeviceId(APP.store.getState());
             return availableVideoInputDevices[0].deviceId;
         }
     } else if (selectedVideoInputDevice
-            && selectedVideoInputDeviceId !== localVideo.getDeviceId()) {
+            && selectedVideoInputDeviceId !== localVideo.getDeviceId()
+            && !newLabel) {
         // And here we handle case when we already have some device working,
         // but we plug-in a "preferred" (previously selected in settings, stored
         // in local storage) device.
             newDevices,
             isSharingScreen,
             localVideo,
-            localAudio) {
+            localAudio,
+            newLabels) {
         return {
-            audioinput: getNewAudioInputDevice(newDevices, localAudio),
-            videoinput: isSharingScreen ? undefined : getNewVideoInputDevice(newDevices, localVideo),
+            audioinput: getNewAudioInputDevice(newDevices, localAudio, newLabels),
+            videoinput: isSharingScreen ? undefined : getNewVideoInputDevice(newDevices, localVideo, newLabels),
             audiooutput: getNewAudioOutputDevice(newDevices)
         };
     },
 
+    /**
+     * Checks if the only difference between an object of known devices compared
+     * to an array of new devices are only the labels for the devices.
+     * @param {Object} oldDevices
+     * @param {MediaDeviceInfo[]} newDevices
+     * @returns {boolean}
+     */
+    newDeviceListAddedLabelsOnly(oldDevices, newDevices) {
+        const oldDevicesFlattend = oldDevices.audioInput.concat(oldDevices.audioOutput).concat(oldDevices.videoInput);
+
+        if (oldDevicesFlattend.length !== newDevices.length) {
+            return false;
+        }
+        oldDevicesFlattend.forEach(oldDevice => {
+            if (oldDevice.label !== '') {
+                return false;
+            }
+            const newDevice = newDevices.find(nd => nd.deviceId === oldDevice.deviceId);
+
+            if (!newDevice || newDevice.label === '') {
+                return false;
+            }
+        });
+
+        return true;
+    },
+
     /**
      * Tries to create new local tracks for new devices obtained after device
      * list changed. Shows error dialog in case of failures.