add id for firefox

Author: aboutsimon

manifest.json

@@ -3,6 +3,11 @@
   "name": "Trektor",
   "description": "Browser-Extension zum automatischen Anlegen von Toggl tracking tasks",
   "version": "0.0.1",
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "trektor@aboutsource.net"
+    }
+  },
   "icons": {
     "64": "icons/64.png"
   },