chore: update firefox manifest version

Author: Akryum

packages/shell-firefox/manifest.json

@@ -1,7 +1,7 @@
 {
   "name": "Vue.js devtools",
-  "version": "6.5.1",
-  "version_name": "6.5.1",
+  "version": "6.6.0",
+  "version_name": "6.6.0",
   "description": "Browser DevTools extension for debugging Vue.js applications.",
   "manifest_version": 2,
   "icons": {