Firefox: implement toolbar button and popup

platform/firefox/bootstrap.js

@@ -39,9 +39,7 @@ function shutdown(data, reason) {
     }
 }
 
-function install() {
 // https://bugzil.la/719376
-    Services.strings.flushBundles();
-}
+function install() Services.strings.flushBundles();
 
 function uninstall() {}