themes: add "NewFox" (#318)

Author: Mr-the-beginner

themes.json

@@ -2221,5 +2221,14 @@
     "pushed_at": "2025-12-05T07:18:55Z",
     "stargazers_count": 14,
     "avatar": "https://avatars.githubusercontent.com/u/204603744?v=4"
+  },
+    {
+    "title": "NewFox",
+    "link": "https://github.com/Mr-the-beginner/NewFox",
+    "description": "A minimal Firefox theme with userContent and userChrome.",
+    "image": "https://raw.githubusercontent.com/Mr-the-beginner/NewFox/main/Screenshot.png",
+    "tags": [ "Mr-the-beginner", "theme type: Auto", "minimal", "lightweight"],
+    "repository": "https://github.com/Mr-the-beginner/NewFox"
   }
-]
+]
+