Add new app config audioOutputSupportedBrowsers and tidy

app/public/config/config.example.js

@@ -25,6 +25,16 @@ var config =
 		{ scaleResolutionDownBy: 2 },
 		{ scaleResolutionDownBy: 1 }
 	],
+	/**
+	 * White listing browsers that support audio output device selection.
+	 * It is not yet fully implemented in Firefox.
+	 * See: https://bugzilla.mozilla.org/show_bug.cgi?id=1498512
+	 */
+	audioOutputSupportedBrowsers :
+	[
+		'chrome', 
+		'opera'
+	],
 	// Socket.io request timeout
 	requestTimeout   : 10000,
 	transportOptions :

app/src/components/Settings/Settings.js

@@ -234,7 +234,9 @@ const Settings = ({
 					</FormHelperText>
 				</FormControl>
 			</form>
-			{ browser.name === 'chrome' &&
+			{ 	
+				window.config.audioOutputSupportedBrowsers && 
+				window.config.audioOutputSupportedBrowsers.includes(browser.name) &&
 				<form className={classes.setting} autoComplete='off'>
 					<FormControl className={classes.formControl}>
 						<Select
@@ -426,7 +428,7 @@ const mapStateToProps = (state) =>
 		me       : state.me,
 		room     : state.room,
 		settings : state.settings,
-		browser  : state.me.browser,
+		browser  : state.me.browser
 	};
 };