feat: add firefox extension

extensions/mal-firefox/manifest.json

@@ -0,0 +1,18 @@
+{
+  "manifest_version": 3,
+  "name": "MyAnimeList",
+  "version": "0.1.0",
+  "description": "Right-click selected anime titles and add them to your watchlist.",
+  "permissions": ["contextMenus", "storage"],
+  "host_permissions": ["<all_urls>"],
+  "background": {
+    "scripts": ["background.js"]
+  },
+  "action": {
+    "default_title": "MAL Watchlist",
+    "default_popup": "popup.html"
+  },
+  "icons": {
+    "48": "icon.svg"
+  }
+}