Add applications key

commands/manifest.json

@@ -4,6 +4,14 @@
   "homepage_url": "https://github.com/mdn/webextensions-examples/tree/master/commands",
   "manifest_version": 2,
   "version": "1.0",
+
+  "applications": {
+    "gecko": {
+      "id": "commands-demo@mozilla.org",
+      "strict_min_version": "60.0b5"
+    }
+  },
+
   "background": {
     "scripts": ["background.js"]
   },